Sorry, but no. Sure, get rid of the classes but things won't be "custom" because there's going to be a "Best Build" and if you don't have it, you won't be wanted. It's that simple. If there was a great deal of customization to classes, it would throw them off balance. It's just how it goes, it can't be done while also keeping balance.

Also, a big difference between two players isn't gear, it's how well they play. Well geared doesn't mean well played.