As for Gasquet's backhand - the stroke itself is fantastic. The problem is his mindset and court positioning. No one is going to consistently dominate rallies on the backhand standing 2 metres behind the baseline hitting the ball below net height.
While the Nalbandian-Gasquet head to head is very one-sided, and Nalbandian has often dominated Gasquet in cross court backhand rallies, it doesn't tell the whole story. Nalbandian's court-position + superior forehand gives him something of a 'handicap' in these type of rallies. Still Gasquet manages to reel off some tasty winners (usually when the match is already lost and he can't be arsed doing his 10 feet behind the baseline act).
While Gasquet's backhand swing is very long I don't think it would be so prohibitive if he had a different forehand technique and mentality. While his highlight reel winners have probably caused some to overrate the shot, it's still very rare to see him shank or mishit on that side, even when he chooses to take it on the rise (unlike another famous one-hander who has a far shorter swing).