It sounds like you've played are poke or sustained damage mages. Any reason why?
Finding a main is about figuring out HOW you want to win, and then finding a champ that lets you do that. I like playing objectives and taking towers, while keeping the enemy down rather than getting myself ahead. I love nunu jungle, but drifted away from jungle this season, and for a bit I played cho'gath before he got popular, but couldn't manage to win w/ him (3-8 in ranked), and looked for other stuff. Found Heimer eventually and love him. Fast pushes great, can poke and bully and build lead through CS differential rather than just having to kill them or make out plays, and has great zoning for objectives with turrets/takes them really fast w/ turrets (plus he can steal w/ ult+w).
It's not about liking his kit (honestly figuring out his e skill shot still is a pain for me and I don't know that I like it), but I love what his kit is designed to do, so I'm willing to get better w/ the kit bc it lets me play the way I want. I'd say you need to figure out how you like to play before you can get good advice on a champ that can do that.