IMO, folding space and wormhole travel aren't "fast" because they aren't based on speed. Certainly a fast way to get to a destination, but it isn't based on the ship being "fast" in itself. The Dune navigator ships were mainly just barges, weren't they? No real propulsion at all. I could be wrong, it's been 20 years. You could count the Star Trek transporter as being "fast" otherwise.
The Guild Heighliners had drive systems which propelled them normally and fold space. The navigator was required to safely guide the ship through the folded space. The Dune House novels gives some more background on how the Heighliners function.
