Apparently having multiple gears is redundant :)
Some courses actually lend themselves to single speed, and a geared bike has only an incremental advantage on a few straights. The super fast girls can take advantage of this on their geared bike. I'm pretty good on all of the technical and twisty stuff so I make up for the lack of gears there, but I'll spin out on the straights. The women's sport category are the intermediate riders so many times I can either win or land in the top 3, but I typically can never beat any of the elite riders which race at the same time as the "sport" cat. One wonders how I might be doing this year if I chose to race my geared cx bike?
It would likely depend on the course, as you said.