I dont see the problem in end-game being about gear-farming.
I see a problem in trying to extend the end-game on a single character, through multiple tiers of the same items (ancients etc), and endless post-lvling systems like paragon.
It is a games as service (including MMOs) sickness tbh. Games dont have to last through endless grind. It is okay to be able to finish something.
Let the endless replayability (which really should be a goal in A-RPG design) come from being able to make new characters, new builds, new playstyles to have fun with.
A-RPGs should have more in common with Civilization, than with WoW. Replayability through actually restarting the game from scratch (no, not talking seasons, just new characters), not through an endless grindy journey.
A journey needs a beginning, but most certainly also an end.
On the other hand, even a single character should have a decent long journey ahead of it, if you want to take it all the way. Hundreds of hours maybe.
Partly through lvling, which should take a fair amount of time. 10-20 hours maybe? Doesn’t have to be that long, if the goal is to encourage multiple chars.
Partly through gear farming - just get away from the extreme BIS item design of D3 - end-game gear should be more open-ended, and perfect gear shouldn’t be needed to complete anything in the game.
Partly through the end-game “progression”. PoE has really set the gold standard here. Make end-game feel like something you progress through, something with an actual end-goal. Not just endless repetitiveness. Moving toward that unique super end-boss is way more rewarding than moving toward “GRift 150, same as GRift 1”.
Heck, take inspiration from the season journey in D3 as well. Give us a bunch of challenges we can go for, that leads us through all the different aspects of end-game, with rewards along the way (this can also be a much better replacement for Paragon lvling. ‘Go kill Diablo with 5 random affixes’, or ‘Finish a Key Dungeon tier 10 without dying’ sounds more fun as goals than ‘go farm 15 billion XP’. And, do not make that journey account-wide. The whole point here should be that it was something you might want to try with different characters and builds.