Balance is at an all-time high- More champions than ever are acceptable for their roles!
People like to complain that the balance team sucks. But, they're wrong - The game is in a better state of balance than it has ever been. The meta is extremely healthy and promotes a wide variety of teams / comps: Here are some examples:
TOP LANE VIABLE PICKS:

And this isn't even including picks like Shen or Trundle that are recently viable.
MID LANE:

You could probably add Kayle and Azir into that list too, but I haven't though they're really strong
JUNGLE:

This isn't even adding in the solo queue champions like Udyr that still excel
SUPPORT:

Karma, Soraka, Sona in great spots but didn't add them to appease population [also if you think bard is bad I got news for you, you're going to be real upset in a month or two]
ADC:

You can at least play eight different, unique champions for every role.
??
Balance is at an all time high wtf stop complaining
EDIT: This guy makes a pretty great post
snippet Katarina is extremely strong and hard to deal with at lower levels of play for example, but players feel like Riot does not care because she's not a problem in the LCS as people know how to deal with her. On the opposite spectrum, the idea of overloaded kits is discussed a lot and I think the worst offender right now is Kalista. She has much too much objective control and is one of the slipperiest champions in the game. With an ult that gives her support more leeway to go ham, free vision of the river, and uncapped damage on her rend, it is a bit much. Honestly, the Rend should be capped somewhere to make her less of a Dragon/Baron controller (as she can out"smite" a Nunu at this point).
I will agree that champion diversity is high right now, but players want the balance team to take care of a few problem champions that they don't like to play against. I think they will get to some of these champions at some point, but balance is difficult across all levels of play, and the balance team will get better.