I have an Issue

I have an issue with learning new champions. I am generally a support main, and in that, I main Leona almost solely. My problem is learning new champions, or relearning champions I haven't played in a while. While I am currently unranked, I have been playing with high silvers/low golds for some time now. Her inlies the problem. I cannot play someone like Diana or Yasuo at a high level because I am not mechanically skilled enough to be on par with these high (and sometimes low) silver players. Now before you say, "Oh, well just go into a bot game." I could play just about any single champion I want in a bot game, and I am guaranteed to do well. Bots are simply not good enough. I wouldn't even say that they are decent for skillshot practice. So, basically my question is, do I continuously play normals with a champion I am not quite good at until I git gud with him/her/it? I would definitely like some advice on how to handle this situation.