For me, I enjoyed D4 as a nice campaign. Played through a few times, once with my partner and another solo.
D4 pros: Impeccable game feel, moment to moment combat, graphics and even some nice storytelling. Enjoy the QoL features for alts and the myriad of endgame loops; Helltides are a lot of fun.
D4 cons: Dungeons are boring to me. Builds that feel fun and powerful are limited to 0-2 per class; a big letdown. Weird network / instance lag which stands out among the otherwise polished aesthetic. Middling open world re: exploration to reward ratio.
PoE pros: Deeeeeep. Hardcore. Aspirational? Still haven't cleared the campaign despite getting closer each league. Lots of builds and skill variety.
PoE cons: Feels like the oldest baguette ever to exist. Wildly stiff gameplay. Ugh its such shit compared to D4. Like DMC vs Skyrim level of difference. Disparate, cheap feeling UI and tacked on storytelling. Exudes HardXCore__Statzz.xls energy and feels practically impossible to navigate a viable build without a guide.
In the end I think Grim Dawn outplays both D4 and PoE. Check it out if you love ARPGs