Cuphead and Vampire Survivors I think are pretty bad fits but you mentioned this about Armored Core too and with that and Nier I think "3D bullet hell" is a reasonable designation
and Returnal I guess, I never actually got to the parts of that that people call bullet hell and it's so weird to me to imagine because what I played of it was so slow--
The Japanese "danmaku" is a bit more apt than 'bullet hell' for those broad sweeps of "lots of bullets but no dodging", because it literally translates to 'bullet curtain'
murkrows: ironically before people started insisting on 'platformer' describing all mascot games (from obstacle course games to collectathons and everything in between) it was just 'action game' which may have been too broad but like, it's also more consistently true
this is what I think when I say bullet hell
platformer
platformer