Luffy and co. still have a lot of room to grow. Luffy can upgrade even more his ACoC (e.g.: with CoO killing, for example) and the others their haki (CoC/CoA/CoO, none of them have everything perfected).
Roger's crew isn't really that much overpowered, I think, with the exception of its core members. If you take a look at old Crocus, for example, he was struggling with the Baroque Works (he didn't want to get rid of them because he didn't want more to come) and was barely capable of protecting Laboon from Mr. 9 and Miss Wednesday/Vivi (if Luffy wasn't there, they would probably succeed in taking down Laboon from the inside). Quite a different portrayal from old Rayleigh, who's still capable of holding his own against the likes of Blackbeard and Kizaru.