Going back to MMOs, players frequently claim that one class is overpowered, usually one they don't play, and another class is underpowered, usually one they play, when the apparent differences between the classes' powerlevels is essentially a 'learn to play and stfu noob' issue. On the small scale of tabletop games, when you aren't usually directly competing against characters played by other people(not counting the DM) the OPness or UPness of the classes it not as apparent.