First off, neither Sherman nor Revis should be the measuring stick for cornerbacks. Good players, but overrated and overexposed in the media. Patrick peterson is the best cb in the game.
Secondly, it's possible that Gilmore ends up being somewhere between a bust and the best corner in the league. It doesn't always have to be one or the other. Like leodis, he's got a lot of raw skill that needs to be harnessed. Luckily he seems a bit brighter than mckelvin (not a high bar, admittedly) so there's a good chance we have a pretty good player here. Give the guy a break. He's been pretty good all things considered.