Yeah for ultra DPS look at ele hit stuff, where they drop 25% off each boss in like 3shots each, DonTheCrown or whatever has a video of this I think I watched, or maybe it was another guy.
Can also look at cute dog's 2.5k hp uber elder kill with arc trapper. Mind you, obviously not deathless, but he somehow manages to do it which is pretty funny.
The massive mitigation tanks killing bosses slowly isn't really new though, it isn't like a recent poe thing. Even back in the old days you had builds that were made to tank various boss slams and shit. It got worse over time as more and more gear is added that increases max resist and convert damage into elem damage mostly and that's kinda meh but ultimately it's not new, you had for a while the aurora aegis shit, max block max spellblock chars, prenerf kaom 12k health chars, prenerf ES 13k low life shav builds and so on. GGG always has to nerf shit over time once it got too good. Remember when you could perma stun bosses because you had 100%treshold? Or perma freeze them with prolif freezing mine?
But while it looks pretty boring, that's always been PoE's strength imo, the fact that with smart building and enough investment, you can make some really crazy shit that feels like it breaks the game. There's enough depth and freedom on the mechanics to let you do that.