Usually when you get near end game the amount of high tier content to do is plentiful and makes the grind between post campaign - end game worth while. However in Diablo 4 you get through what was imo a very enjoyable campaign then from 50-70 is a long grind of renown/map clear but, then you get stoked to do lvl 70 capstone only to not get any better gear and then to find out all you get is a new world tier lvl but, have fun grinding same dungeons over n over till 100 so basically post campaign is heavy heavy repetitiveness that actually destroys the excitement a player has once campaign is over. Instead of jumping into a post campaign world of a lot of activity you just back track all over doing helltides that are a snooze fest, increase tier in nightmare dungeon and grind dungeons/mobs for levels and paragon points. This is worse grind than New World which is a full MMO and that was awful in questing.
It’s a brand new game, it needs more time to add content.
Meanwhile Nintendo releases ToTK as a complete game, so what do I know.
On a horribly outdated system. Every company has their flaws I guess 
Yeah it’s boring, endgame is lacking atm. However maybe you want to try the pinnacle boss lilith at 100 or try other classes to get a feel for them.
ToTK was really enjoyable. All these days I keep thinking I should just drop D4 and return to zelda to finish some of the sidequests -)