LightNovels

tl;dr If you liked Megumin, you will likely enjoy Konosuba

Not sure how helpful this will be since I have not read the LNs you listed in your post, but I am up to date on the manga adaptations of both Spider and Loner Life. Also, I am currently reading the Konosuba novels (currently in vol 3), but have watched the anime adaptation (the LNs are very similar in tone to the anime so far).

I would say that if you liked the Megumin anime, then you are likely to enjoy the main series as well. Compared to the Megumin spinoff, the main series is probably a bit sillier and comedy focused. The Megumin series had some serious moments focusing on the friendship/rivalry between Megumin and Yunyun as well as some hinted serious plot underlying Chomosuke and the antagonists of the show. Compared to this, the main Konosuba series is more comedy-focused, often setting up a scene or scenario that seems serious or dangerous, only to then undercut it with humor or a gag. Compared to Spider and Loner Life, this is really the best comparison to Konosuba. At the end of the day, the joke always comes first for Konosuba. This is both a blessing and a curse. It is genuinely funny, probably the funniest LN I have read, but at the same time, that humor can undercut the ostensibly serious circumstances that the characters are going through.

Compared directly with spider (via my manga exposure), it is much sillier. Kumoko can be a silly protagonist, especially when the parallel minds are involved, but at the end of the day, she is seriously fighting for survival with life/death stakes. We also see Kumoko come very close to death on more than one occasion. In Konosuba, these stakes are never portrayed as dire or desperate in the same way. In fact, (I am being vague to try not to spoil) the prospect of death becomes a bit of a running gag in the series.

Compared to Loner Life (again via my manga exposure), Konosuba has a better fleshed-out cast of characters in my opinion. It might just be the manga adaptation, but Loner LIfe tends to almost exclusively focus on Haruka and his (usually solo) exploits (I guess since he is the titular loner). Other characters are often doing things off screen and are given thin, mostly archetypal characterization. Konosuba is more of an ensemble comedy in which a group of characters are each fleshed out in ways that then interact with each other to produce jokes. It is a similar formula to comedy ensembles even in Western media (Always Sunny, Brooklyn Nine-Nine, etc.).

I realize now how much I have written, so I will add a tl;dr at the top. If you want to get a taste, just try a couple episodes of the anime. The LNs I have read so far are very similar in tone and I believe the show would set your expectations accurately for the LNs.