It doesn't seem to me that when balancing existing characters or making new characters, that the developers really think about not only how to balance characters compared to other characters, but to think of each character and say:
"what does this character bring to the team, or why should I use this character over that character?"
As it is, there are some characters that just don't bring enough to the team to warrant using over other heroes that bring more. And there are some that if they are on your team, and the person playing is any good, it drastically increases your chance of victory, these are considered top tier heroes.
For example, if I'm playing an a team, why would I use Worwick over Trynd? or why would I use ash over sivir? or Kat over Yi? or Eve over Twitch? Or in top tier play is there any reason to have a pirate on your team? or an Udyr? Janna? These characters may do well but when it comes down to which is better for the team it's pretty clear.
Basically what I'm saying is that when we get to ranked ladder play, its going to be every team using maybe different setups of around 10 champions because some champions bring way to much to the table to not have and some, while maybe not underpowered, just don't bring as much as another champion.
So I think when the developers are re-balancing old champions and making new ones they really need to consider what the champion has to offer a top tier team because having 40+ playable champions doesn't matter if they aren't viable to top tier play.