Despite many tier lists Kayle is doing fine at each elo. Tier lists are fine for judging a players perception, but they don't do a good job at looking at actual power or balance.
A good example we are seeing is pro play is Singed and Seedjar both being frequent picks when tier lists and the general player base thought both were garbage. Now obviously pro play isn't 1:1 with solo que, but our data shows that both are doing fine in solo que as well.
Every tier list is going to have someone at the bottom, that is the nature of lists. That doesn't mean that someone is in a terrible spot though, even if the list were an accurate representation of general power. There aren't any champions that I would say are in a super bad spot, as far as I am aware, and if you enjoy playing a champion you should keep playing them.
With all that said I'm not on the balance team, and was on vacation this last week, so I might be a little out of the loop.