I always took the Vegeta/Cabba fight as Vegeta playing around or just underestimating Cabba slightly. I never took it as Vegeta actually being serious, because the moment he gets serious Cabba goes on the defensive and is then out once Blue enters the picture. It was more like Vegeta was just seeing what he had, got more than he expected, and then just ended it.
I know the U6 Saiyans have higher base forms, but I feel they still shouldn't be near Goku/Vegeta's levels, a step below sure, but not there, which I feel SSJ2 helps drive that point home a little more.
But I mean personal opinions at the end of the day really over it. Most things are irrelevant beyond Blue anymore, and I guess Legendary now.