Well you said he wasn't a believable superstar actor and lazy in real life and on the show. I can't comment on Adrian Grenier (besides, he may be type cast) but in the show, he didn't want to be a superstar actor. He wanted to be an indie-actor and was only driven by the projects that he had a passion for. He wasn't chasing Hollywood, unlike his brother, who was trying to be in everything to keep his name out there. Ari is the one that pushed for him to be a superstar because he was a natural, likable and a pretty boy. If you didn't believe him as an actor, did you believe them as real friends? That's what the whole show was about; their interaction with each other.
And as for the show not making you want to see something with him in real life, you do know that Entourage was a parody, right? Johnny Drama's career is damn near identical to Kevin Dillon's career.
You really said Dana Gordon? She had like 10 lines, 8 of them in one episode. Shawna was just as much as a memorable character as Dana Gordon.
Might as well said Josh Weinstein