That entire buu thing where one can hurt the other is bs
I mean it should apply to everybody. Force him to regenerate to many times and you can get him tired and exhausted
And this is precisely what anime did with Vegeta and Buuhan fight. The guy got so beat up his regen started to become less...
Vegeta should win, but with toyo writing you never know. Gas already stated Bardock was stronger than a low class saiyan and then he got that emotion boost as well
It makes no sense for Vegeta to be stronger than the fusion of him and Goku. Yes sure he is using form one level higher and powered up from training but still.