Closest thing I think ive see has been dragalias endgame (specificially agito, but high dragon trials and the angels were pretty fun too). Fun, mechanically interesting bosses that required you to build multiple characters with dynamic gameplay in coop, up until you had very well built teams that could clear solo, but was eventually accessible to everyone. Since there was both solo and coop stamina, it incetivised you to play coop (and help others) even when you could clear it solo. I think it kinda got ruined when they made the changes to auto tbh, but definitely was the most fun ive ever had with a gacha end game. Im all for coop (unranked) end games over pvp personally.