Tremonti can do a lot of things that we don't know about. Bill Peck (Tremo's shredding friend) said that Creed fans would be very surprised if they knew what Mark is capable of. (or something along the lines of that, I've forgotten the actual quote)
I think what Mark does is play for the song, not for showing off. Obviously, who would want to hear endless wank after another when it doesn't fit in with the song/subject matter.
So no, I don't think he is being held back (obviously he has a lot of talent and skill), I think he's just playing these riffs because it fits.
________
Buy Herbalaire
________
LovelyWendie99