What if sets were idols, kind of like legends of the hidden temple silver monkey, low level weaker sets require 2 “fragments” or runes maybe at the forge and you craft a set idol that has stats, BIS sets could be 4 runes or frags at the forge and it makes a 2x2 or 4x1 of 4 diaganol idol with cool stats then no gear slots messed with and you get cool bonuses if you find all the pieces of the set and assemble it you could have 4 peices is weird shapes that mess with what other idols you can slot in for balances and maybe obly 1 set idol at a time
They could also do the assembly as a new dungeon with its own key and after you kill the boss you go to an eternal forge or something like you make legendaries now, but instead you slot in your set fragments tonforge the set, then like level one dungeon can only do 2 peice sets, level 2 can do 3 frags, 3 does 4 frags and the fourth level does 5 peice sets and they can make basically tetris peices for the idols inventory for balances and whatnots