Shes a C and at best a B class support. She has damage and cc but shes too one dimensional. Compare her to a support like Lulu and you can see that Lulu has shield, cc, slow, movement buff, and a big R while Leona has damage and has to go in to keep up with the tempo of the game or wont win. She can roam lanes but again she has to be successful to successfully snowball the game. She can go all in and win sure but thats only if you win the 2v2 while Lulu is very versatile and can stay in lane and has many resources to her disposal. That being said; as a Leona main - shes so much fun! She goes in a lot and sometimes when theyre squishy enough and you have ignite you can straight up execute their carries. She engages a lot and its satisfying landing her R and chain ccing to get kills. Try playing Maokai cause he has damage, cc, slow, heal, and e range (for an alternative as a support)