I think to say someone is overachieved or underachieved, is based on the expectation of them. So you won't say Tsonga or Gasquet reach their expectation so far, since they were both exceptional juniors and were expected to win slam. As compare to Gilles, who wasn't expected to even make pro when he was a junior.
Exactly. News-Tennis83 is certainly entitled to his opinion, but I just absolutely cannot agree with the notion that Gilles has not over-achieved in his career. Nobody expected this lanky kid with chicken legs from a non-athletic family to ever beat the likes of Federer (twice), Djokovic, and Nadal (in Madrid no less) ever let alone all in the same year. The only other player to do that was Andy Murray who's now top 4 himself and part of that click. Not to mention get as high as 6 in the world with no weapons or a serve that would win him easy points and get him out of trouble regularly. Pretty impressive for a kid from Nice that was told he'd never make it far in the sport and pretty descriptive of an over-achiever. And hopefully, he's got a few more tricks up his sleeve before he calls it quits.