In season three of "Star Trek: Discovery," Captain Saru makes a somewhat surprising decision and appoints Ensign Sylvia Tilly as his acting first officer. This was a source of considerable debate at the time, particularly in light of the mission to the Verubin Nebula at the end of the season.
Now that quite a bit of time has passed, I wanted to revisit the events of that mission and evaluate the decisions Tilly made while in command of Discovery. I've broken each significant decision or order down according to the following criteria: the circumstances under which the decision was made, what the decision was, and what the general outcome. I've tried to reserve my personal judgment until the end.
Episode: "Su'Kal"
Circumstances: The USS Discovery discovers the source of the Burn - a planet in the Verubin Nebula featuring a massive dilithium deposit, as well as a crashed ship with a Kelpien life sign aboard. The Verubin Nebula is difficult to navigate, and contains deadly radiation and harmful electromagnetic fields.
Command Decision: Captain Saru chooses to lead the away team, leaving Ensign Tilly in command of Discovery.
Outcome: Admiral Vance expresses misgivings, but allows this plan to proceed. He also reveals that the Emerald Chain appears to be attacking Kaminar in order to lure Discovery there to obtain the spore drive.
Circumstances: Discovery jumps into a stable pocket of space within the nebula, which affects the ship's shields - a three-hour repair job, according to Tilly. The away team beams to the planet.
Command Decision: Tilly assumes command and jumps Discovery out of the nebula.
Outcome: Discovery is able to avoid further damage and commence repairs to the shields while the away team is on the surface. Innoculated against the radiation, the away team is able to spend a maximum of four hours on the planet.
Circumstances: While the shields are being repaired, Commander Burnham reports that the away team has found something and growling. Communication with the away team is then lost.
Command Decision: Tilly orders Commander Stamets to prioritize the shield repairs, diverting power from other systems as needed, so they can retrieve the away team.
Outcome: The shield repairs are accelerated. Shortly after this order, an unidentified Federation ship is detected on long-range sensors. Ten minutes out, it does not respond to hails, but sends correct response codes.
Circumstances: With the unidentified ship now two minutes out, the crew discusses how the vessel's presence in the region doesn't really make sense.
Command Decision: Tilly orders Owosekun to scan the area around the ship.
Outcome: The crew discovers that the approaching ship is, in fact, the Viridian, as no one else has the motivation and the means to travel such a distance.
Circumstances: The Viridian arrives at Discovery's location.
Command Decision: Tilly orders red alert. Rejecting the possibility of retreating via transwarp tunnel or spore drive, as it would leave the away team vulnerable, Tilly orders Discovery to cloak.
Outcome: This successfully hides Discovery from the Viridian, though it also deprives them of the ability to use the spore drive. The Viridian cloaks as well.
Circumstances: The crew ascertains that Osyraa must be able to track Discovery's jumps, and that she must require the ship, as she didn't open fire immediately upon arrival. Stamets reports that Discovery cannot jump for another 30 minutes. Osyraa hails Discovery.
Command Decision: Tilly orders Stamets to find a way to repair the shields in the next ten minutes. On a comm channel, Osyraa claims to want Discovery and her crew for "leverage."
Outcome: Repairs to the shields continue to be prioritized as the situation escalates.
Circumstances: Unbeknownst to either ship, Su'Kal creates a spatial disturbance, destabilizing Discovery's dilithium. Discovery's engineering team is able to contain the effects, but both Discovery and Viridian lose their cloaks.
Command Decision: Tilly orders weapons ready.
Outcome: The situation with the Viridian continues to escalate.
Circumstances: Discovery's shields have been repaired to 54% as the standoff with the Viridian continues.
Command Decision: Tilly orders Stamets to prepare to jump Discovery to safety, rather than allow it to fall into Osyraa's hands. Booker volunteers to remain behind in his own ship to retrieve the away team.
Outcome: Over the protests of Stamets, this plan is put into action.
Circumstances: Osyraa hails Discovery again. Osyraa notes that Discovery has not yet jumped away, and deduces that Captain Saru must be in the nebula. She also claims that the structural weakness in Viridian that Discovery exploited in "The Sanctuary" has been repaired. Booker leaves the shuttlebay in his ship.
Command Decision: Tilly orders the spore jump.
Outcome: Emerald Chain soldiers beam into the engineering lab and attack Stamets before he is able to follow this order. Viridian ensnares Discovery with some kind of tendrils, and Emerald Chain soldiers begin capture the ship. Ultimately, they are able to take the bridge and remove Tilly from command, jumping away just as Booker and Burnham emerge from the nebula in Booker's ship.
Episode: "There Is A Tide..."
Circumstances: The Discovery bridge crew are being held in the ready room by the Emerald Chain.
Command Decision: Tilly demands that the rest of the crew be released, volunteering to be held as leverage as acting captain.
Outcome: Zareh, the Emerald Chain soldier encountered by Tilly in "Far From Home," flatly refuses, and mocks how easily they were able to capture Discovery.
Circumstances: Having captured Booker, the Emerald Chain escort him to the ready room.
Command Decision: None
Outcome: While Tilly gives no orders here, she is able to silently confirm that Burnham is somewhere on Discovery, uncaptured.
Circumstances: A squabble erupts amongst the hostages when Rhys and Bryce are caught using Morse code to communicate. This, in turn, diverts the guards' attention.
Command Decision: The Morse code is revealed as ruse, as Tilly and the crew attack and incapacitate the guards. Tilly orders the crew to regain computer control and monitor communications, with the goal of retaking the ship and returning to the nebula to rescue the away team.
Outcome: Having turned the tables on their captors, the crew are now able to attempt to regain control over Discovery.
Circumstances: Having gained access to some of Discovery's systems, the crew discovers that the Emerald Chain are closing in on Burnham's position.
Command Decision: Tilly orders Ryn to scramble communications to help Burnham as much as possible.
Outcome: This is a helpful move, and Burnham is able to continue on, having defeated one Emerald Chain solder and taken his communicator, which she uses to mock the Emerald Chain and signal to the rest of the crew that she's still alive.
Circumstances: Burnham remains at large on Discovery, with the Emerald Chain mobilizing to find her.
Command Decision: Ryn scrambles Discovery's internal sensors as the bridge crew escapes the ready room. Booker and Ryn remain behind to fight off the inevitable search party.
Outcome: The bridge crew are now able to navigate the ship with some degree of freedom.
Circumstances: The Discovery crew make their way to the armory and arm themselves.
Command Decision: Tilly orders the crew to take the bridge at all costs.
Outcome: Three DOT-23 drones arrive, and Tilly realizes they are being controlled by the sphere data.
Episode: "That Hope Is You, Part 2"
Circumstances: As the situation on Discovery deteriorates and Tilly's team fights their way through the ship, Osyraa orders the life support systems disabled and the atmosphere drained, leaving the crew with approximately 30 minutes of consciousness. Burnham transmits a cryptic message over comms.
Command Decision: Tilly recognizes the message as an instruction for her to destabilize the superconductors holding one of Discovery's detached nacelles in place, which will knock the ship out of warp and allow Starfleet to overtake it.
Outcome: With the DOT drones unable to function in the intense magnetic fields, the crew sets out to enact this plan.
Circumstances: The crew, save for Owosekun, are unable to proceed any further due to oxygen deprivation.
Command Decision: Tilly orders Owosekun to take the remaining oxygen and detonate the bomb on her own.
Outcome: Owosekun proceeds, leaving the rest of the crew in the corridor. The bomb is sucessfully detonated, and Discovery is forced out of warp. However, the Viridian is able to take the entire ship into itself before Starfleet arrives. Meanwhile, Burnham and Booker are able to defeat Osyraa and retake the bridge.
Circumstances: The unconscious crew have awoken and returned to the bridge. Burnham tells Tilly she has an idea of how to proceed.
Command Decision: Tilly relinquishes command to Burnham.
Overall, I think Ensign Tilly did quite well while in command. She had multiple priorities to juggle early in the mission, with the dual objectives of protecting the away team and protecting Discovery from Osyraa. Ultimately, it was a bit of a no-win scenario, as abandoning the away team on a massive dilithium deposit at the very source of the Burn could have had devastating long-term effects, as could allowing Discovery to be captured.
Of course, Discovery was in a weakened state, and ultimately was captured. Once that happened, Tilly's leadership was admirable. She prioritized her crew when she could, but was also willing to make tough calls and send them into dangerous situations when she had to. Her determination and ingenuity allowed the crew to ultimately retake Discovery and rescue the away team.
I concur with your conclusions. In the famous words of Captain Picard, it is possible to make no mistakes and still fail. Tilly did the best she could against a superior opponent, and when the opportunity to turn that defeat around arose, she scraped out a win with casualties minimized, and I think proved herself more prepared for command than the show or fandom generally gave her credit for.
Especially since the Discovery is a comparatively ancient ship with newer hardware just glued on.
Much of its onboard design and technologies (like the hull materials/structure, and core computer systems) are similar to what the ship was originally fitted with, which would be millennium-old designs at that point in time.
A newer starship of the time might have fared better, but Discovery did not have that advantage.