Victorious said:
19 made Vegeta's whole body snap back.and also Vegeta lost his footing a little bit..and 19 drew blood from Vegeta. Gohans tank on FP PC his head bent back but he didnt lose any footing not to mention no blood was drawn. Gohan's tank is easily more impressive so his gap on Cell is bigger than Vegeta's on 19 post. There is no evidence at all Vegeta can one or two shot 19 post.
True what you say about the tanking (I remembered blood in Gohan's mouth after Cell's punch as well, but after checking he already had that blood from his previous beating), but the difference here is that Gohan was going all out in terms of Ki (he wanted to torture Cell, but he wasn't hiding his strength, and in fact he put an effort behind his punches) while Vegeta, on the other hand, wasn't (he didn't go all out until after 18 went all out against him).
Remember that Vegeta had been observing the fight between 19 and Goku, so he knew how strong the android was.
Regarding the evidence of Vegeta being able to one shot 19, we have it. 19 post-absorption was above ill SSJ Goku post-kamehame, but not by a huge margin (Goku could still dodge some hits and connect hits from himself):
http://mangalife.us/read-online/Dragon-Ball-chapter-148-index-2-page-1.html
And that Goku was already much weaker than himself before firing the KameHame (not because of the Kamehame, but because the illness was constantly weakening him), who was already much below the level of a SSJ:
http://mangalife.us/read-online/Dragon-Ball-chapter-147-index-2-page-9.html
On the other hand, this is Trunks & (weakened) Vegeta against 18:
http://mangalife.us/read-online/Dragon-Ball-chapter-160-index-2-page-8.html
If you look at it, Trunks loses his consciousness even before Vegeta, and that Vegeta had already lost "a lot" (in DB terms that could be between 10-15 of his power) of energy in his fight against 18.
So, we have:
SSJ Vegeta >> SSJ Trunks >> ill SSJ Goku (from when Piccolo describes him as "weak") > 19 post-absorption > ill SSJ Goku post Kame-Hame
And we know the difference between Vegeta and Trunks was big, because SSJ Vegeta had (in his peak) a power comparable to Android 18. So if she almost one-shotted him, Vegeta could've done the same if serious about it, and post-KHH #19 was much, much weaker than that.