Certainly losing to Gimelstob is embarassing on any surface, at any time. But you have to remember that COurier´s career at the top was really short, it was pretty much from 1991-95, on any surface. His downhill was really quick. So if we look at that period, only the loss to Olhovskiy seems like a bad one, Stich, Sampras, Forget and Pioline were all excellent players.
Stich and Sampras I acknowledge, but Forget was a Grand Slam mug honestly, and while Pioline was certainly a great and talented player, nothing to gawk at either. Hewitt in general had the better record and lost to more notable players IMO (Djokovic two times, Federer three times, Baghdatis one time, Soderling one time, Roddick one time).