Avoided ranked all year until now, placements taught me I can't play anything now

So last year I made an attempt at a grind and hit plat for the first time, mainly using Gnar and Kled. When Runes Reforged went through, it hit me hard. Without Fervor, I really don't feel comfortable on gnar anymore, and Kled I can't stand to pick blind (and many normal games have made me give up on hoping I won't be picking first). I didn't want to play ranked until I had new comfortable picks or I liked a new patch and it's never happened so I just gave in. I was playing against too many plats and diamonds in normals and I was hoping ranked wouldn't be as bad.

Moved back to mid lane awhile back. Problem now being I only like to play immobile, slow mages and (besides not enjoying replacing Deathfire Touch with Aery or Comet) I'm just incapable of keeping up with all the speedy assassins my opposing laners and junglers keep playing. I simply can't keep up. I don't have the reaction speed to deal with all the "flash-burst-dead" that everyone else keeps doing every game. If I play slow and safe, they just roam or go fight my jungler with theirs, if I try to keep up and play aggressive, ganked by super mobility.

I don't like playing aggressive early levels, but that seems to be when the entire game is won in most games. I've always preferred to farm it out to 1 item and then look for outplays. Now I can't find myself keeping up anymore and don't really know what to do.

I'm terrible at jungle, marksman is too much pressure and playing right next to a rando is too stressful (goes for support too), and if I can't keep up with the hyper-mobile-aggressive mid and top laners everyone is playing....I'm not sure what to play anymore.

As a positive, 3 wins was enough to leave me at Gold V, so I technically don't have to keep playing ranked if I don't want to. I just have to hope finally doing ranked and dropping this far will finally make me stop playing with plats and diamonds in normals. I'm terrible and significantly worse at the game than I was last year, so I wish matchmaking would put me where I belong.