Isn't Roddick enough proof that a big serve+forehand is just not enough any more? The only Slam he ever won was because he was so much more aggressive off the ground (not to mention Federer was just entering his prime). And Roddick is actually better off the ground even at his most passive, explaining how he made all those Slam finals. Isner lost his momentum with his horrid European swing last year, when I was expecting great things from him. He became a servebot in service games + pusher in return games. Not bad results overall, won titles, but never where it really mattered.
Any decent baseliner with a good serve seems capable of beating him.