Tsonga's movement isn't an issue, his shit BH and ROS are. He has the best attacking game in tennis overall along with Federer imo (considering serve, fh, net play, power...), but he leaks too many ridiculous errors with his BH and tanks too many return games to be a genuine top player in this particular era and conditions.
yes, his backhand is related to his poor movement
he does not cover that wing effectively, and does not have a good slice or drive backhand to make up for it
he should be camping in the backhand corner, to hit the big forehand return. he does not do this often enough
i disagree that he would be necessarily better in say, the 90s. yes, his serve and volleys would be even more effective, but that return of serve...can see him winning wimbledon or us once or twice, and that's at a push
more hard court masters, certainly