I've never understood why these threads provoke so much argument.
Isn't the issue here simply that you have a mixed bag of people at 3.5/4.0 level who all look wildly different? Given that players at the 3.5/4.0 level aren't the most consistent, who knows whether you're catching them a good day, bad day or whatever?
The guy in the black shirt has a pretty good if somewhat inconsistent forehand. That's alone is going to take him some way at the 3.5/4.0 levels. His movement isn't that great but he has a good sense of the spots on the court that he wants to hit with his FH. He has a huge hole on his backhand side though which is going to stop him progressing until he shores that up because any savvy opponent is going to hammer that BH. A bird with a broken wing simply doesn't fly very far.
The problem with the video is that he's playing a guy (white shirt) who's half a level lower than him and who doesn't put any pressure on the ball at all. Black shirt *could* be competitive at 4.0 but you never really know until you put a load of these players into a 4.0 league and see what their win/loss ratios are like. What worries about him is the fact that he haemorrhages alot of points when he doesn't need to - he seems to be a real mixed bag of the good, the bad and ugly. But then again looking at similar videos that seems to be what its like at low to mid 4.0. That said, who knows if he's even playing seriously? There's a huge difference between 'park play' and a ratings match with points on the line, people watching, ratings at stake etc.