Major issue here. Blizzard basically believes that sets should be what define character builds, so it's either more sets or rebalancing of current ones. Or more legendaries for the same sets. But that doesn't change the fact that someone will therycraft the shit out of them and everyone will go for the "GR 8169685918659+ best build".
Actually, taking out some exceptions where the set is simply not viable at endgame (lolwastes) other sets are pretty balanced. Problem is some classes have a better synergy and the "meta" will always revolve around the same stuff - there's space for only one #1.
Problem is that Blizzard recently "addressed" the Wastes issues: they're fine with it being crap because ddue to the damage mechanics (tornadoes, rend, etc) servers simply cannot handle it and they're fine with people not playing it. Or in their words they're "happy with the set filling a niche goal".
LINKY HERE
There's a completely different direction between what players want/need and what Blizzard thinks is good for the game. And i suppose it's due to the itemization system which was designed around sets and they don't actually have much room around it until they break everything and redo from scratch.
Atm our and their best bet is the Paragon system. Revamping it is way easier and instead of it being a passive +stats increase table it can become some sort of huge talent tree that grants new powers/effects to our character. This way we will have a major degree of customization with builds and a more interesting reason to play more after we're done with the season journey (or even non season).
And obviusly we need more endgame stuff than GRs. ounties are good only for reagents which you won't need after you've found your items (pretty fast) and the GRs become the best source for everything, not counting the ONLY source for increasing Legendary gems levels.