Originally posted by Kento
Just like you have are taught a style. It's within all their powersets to do the same thing. They just use different attacks because they were taught them by their masters, or in Vegeta's (and probably Future Trunks) case created their own ki attacks. It's because they bulked up. Not one other case has been like that. Every amp of ki has always been speed. Vegeta was owned easily by Zarbon. Him being beaten and healed amped his ki and was able to in return own Zarbon. Gohan got angry during the Radditz part of the Saiyan Saga and his ki skyrocketed and he was able to hit Radditz who was owning Piccolo and Gokou in speed. Gokou went from being Ginyu's level before getting hurt to being able to keep up with Freeza after healing and his ki amp from that no training at all. Vegeta went from loosing to Recoome to fighting Jeice evenly who was even faster than Recoome. Then there is also Piccolo fusing with Kami. That ki amp from being beaten effortlessly to being able to keep up with 17 without any training just a ki amp. Out of all the times ki amping has equaled speed amping twice by people who just bulked up to get strong doesn't negate that ki does equal speed. While how much faster is unknown I think it's safe to say their speed increases at least half of what their power increases. At the very least since they go from being blitzed to being able to blitz after getting more powerful.
Vegeta really had no idea that Zarbon had a second form so he wasn't really prepared for that. The second time they fought, Vegeta was more than prepared since he knew what to expect and he was stronger. And yeah, Gohan was able to hurt Raditz who was faster than Goku and Piccolo, however, that doesn't mean he was faster than Raditz (who was still in shock anyway). Also, if I recall correctly, despite hurting Raditz, Gohan's power level was still lower. And what's so impressive about beaten Jeice? He could have been weaker than Recoome. As for 17 and Piccolo, they barely even fought the first time. 17 got in like, what? Two hits? And it sure wasn't very fast since Krillen was able to see him do them too. That's why we need to go by what we see instead of speculating.