It isn't accurate to say there's no momentum in SRB2. Rather, momentum is severely restricted if you are on ground and not spinning, which sticks out like a sore thumb if you really try experimenting with going at high speeds. You can charge up a full spindash and do a wide jump, perhaps stacking it with a character ability, but as soon as you land on the ground, you're back to the comparatively low max ground speed. This speed cap unfortunately detriments gameplay quite a bit, especially with things like horizontal springs or downward slopes; what's more satisfying than doing a cool aerial stunt in a Sonic game and then landing on the ground running at extra-high speed? SRB2 would certainly benefit from allowing cool stuff like that.