I have #19 post at 60% of SSJ Vegeta. It COULD be less depending on how you see the fat androids' relationship with #20, but I don't think it NEEDS to be. Remember that Vegeta was generally nonchalantly going through #19's defense, punching him into the face, mocking him... he wasn't using effort at all and the only instance he seemed to put some level of effort was when punching (it wasn't exactly a punch, but dunno how to call that) #19 into the ground. #19 wasn't one shotted, sure, but you have to remember that he isn't an organic being, he doesn't feel pain like the others. That's the reason he got up like nothing after receiving a hell of a beatdown by sick Goku's hands, much to Yamcha's surprise. Tenshinhan explained that the reason he isn't affected by it is due to being a robot and consequently not feeling pain or fatigue. Sure that his strength also has a finger on it, but his body consitution also helps a lot.
So the fact that Goku could one-three shot the Ginyus doesn't necessarily mean anything in my book. The Ginyus are organic beings, they feel pain, and the only instance #19 seemed to be agonizing in pain was in an add-in scene in the anime. So I am perfectly fine with Vegeta's gap over #19 being the same as Goku's gap over Ginyu, although yeah, I do have Semi Cell's gap over #16 and #17's gap over Piccolo as considerably above than that (right at a 50/100 gap). Whilst you could still explain away Piccolo being one-shotted, #16 was still fully robot.