Champions have become boring
Generalizing here;
They're all played one way, in one specific role, with little room for successful variation. In season 4/5 there was a lot more options for most every champion. You could take nearly every champion into the jungle and do okay (so long as Lee Singer didn't find you) Most champions could go at least two lanes successfully, particularly versatile champions could go 3, or even 5 roles. (Irelia, Kayle, Nidalee, and a few others) But now a lot of that's been killed off. Lane Kha? Gone. Lane Nidalee? Coma'd. Jungle Brand? Missing. Jungle Riven? Top J4? The list literally goes on.
Then there's versatility in build paths. What happened to things like AD Malz, Bruiser Nid, Tankgar, Tank Riven, Tank Kha, Mid Assassin J4, etc etc etc (list is literally innumerable) Some of this stuff is still playable, sure, but for the most part not neasrly to extent it once was. Before it was off meta but still very much viable. Now? You're basically hamstringing yourself if you don't so much as take the most 'effecient' keystone for your champ
