Are you serious? It's weird how Tsonga is almost never at his best when playing top 4 players. The far more likely conclusion would be that those players are not at their best when Tsonga beats them. But maybe that's too far fetched.
It's not weird at all. If Tsonga had the ability to always be at his best, he'd be in the top 4 himself. As it stands, on average Jo's game is full of holes those players can exploit, namely the worst BH and ROS in the top 10.
The only logical conclusion is that those player's average/normal level is far superior to Tsonga, which is not exactly controversial.
Tsonga is still a matchup neither of them relishes because he can simply blow them off the court on any given day. Performances like vs Nadal at AO 2008 or the last three sets vs Federer at Wimbledon are very rare - if they were the norm, Tsonga would be #1 - but when they do happen there's very little the opponent can do to stop him. On those (rare) days where you can't extract cheap errors off Jo's BH or get tons of free holds due to Jo's horrendous ROS, good luck beating him.