That's pretty much how any moba works, AAers are almost always better than everyone else for damage. Casters tend to be good for one big burst, but unless they outrange AAers it's moot, and Tanks really only are good at pulling Casters, Supports, and other Tanks off their team. AAer's melt everyone.
I remember a match where I ended up playing against a Vikki, as Vikki. We had the same build, and really it just came down to who shot first. Everyone else on both teams weren't threats whatsoever, because we were the only AA damage guys. This is a fundamental 'problem' with Mobas, since AAers almost always get critical damage, and everyone else gets nothing. There's no critical defense, and nothing that makes abilities significantly more powerful. So...Unless you have some idea to bring everyone else up to AAer's level, it'll pretty much come down to who has a better AAer or how many they have.