Having just watched Day 1 and 2 of the HK Sevens I must say Ross has it spot on.
Going into the games Carlin Isles was the name on everyones lips, he's even in the tournament programme as one of the men to watch. He's known now, there was a buzz around the stadium when he got the ball, but he didn't impress. Opponents know him, and know what to do (every team has a fast guy in sevens rugby).
Teams closed him down. In 30mins of rugby he got one run.
USA's first game, against Kenya. He cost them the match and was taken off in the second half. He missed 2 tackles and both times Kenya scored. Missing a tackle in sevens is a big no-no. He scored a try, partly from speed, partly an opponent fumble, but he was aliability in defence and positionally has a lot to learn. His US teammates were clearly not impressed with his lack of physicality.
Game 2 - USA lost to France. Isles played the first half. Didn't get space to run, was closed down the moment the ball came near him. Came off in second half.
Game 3 - USA lost to New Zealand, rather predictably. Again didn't get the open space to use his speed.
The difference between him and the games other fast guys is the lack of power Isles has and the lack of rugby nous. Dan Norton, England's fast man, often has an effective game even when he can't use his pace, because he is a decent defender and has good hands. Isles hasn't yet got the all-round game.
Plus, he's small - 72kg guys don't "dominate" in rugby, evens 7s.