Please just learn how to q and budget your mana.
As someone who started out with Diana, and THEN played those other champs (Barring Fizz, won't even play him during free week.... he makes me foam at the mouth) I will always always feel more rewarded and have more fun for making sweet plays with Diana.
But if you want to go play another champ because you think they are 'broken', or 'ez' , go ahead. Other than Zed, all of those champs actually do take a degree of skill to do more than 'okay' despite what other people say.
I didn't own everybody with lucian the first time playing him, even while he was buff as hell. To this day, I see many fail lucian ults.
I still can't play Yasuo to his full potential, and it's wayyy harder when you've only got yourself to proc your ult. These days I don't want one on my team, and If I see him getting first picked I either laugh or groan depending.
Zed is retarded. While you're figuring out that combo that's actually really easy, you can get away when you fail. 0/10 Had I known, I would have given him the fizz treatment. He is one of those champs that you don't want to go up against if you don't know his kit firsthand, however.
I play AP bruiser Diana when laning. I just buy all AP items that offer defensive stats, along with maybe a randuins/banshees and deathcap. Some people play her with Nashors and lichbane, but that's never been my thing. Some argue it's better for jungling, but after just one or two items camps are a breeze anyway, imo.