That is exactly it. Vegito has too few feats. That's like me saying "Vegito was turned into chocolate and was still conscious and retained his power, when has SBP been turned into something he is not that compares to that feat". Apples and Oranges.
If Prime can survive a Universe exploding what feat does Vegito have that even comes close to proving he can put Prime down for good?
On this site the majority are against DBZ on another site everyone is for DBZ. It's all opinion. Now when it comes to two fighters from the same universe, you can state facts, because more than likely they have fought before so that gives you something to go off of. That and they follow the same laws of physics.
Different universes have different rules. Superman noted that the people in the Marvel U had different heart beats than people from DC. In Dragonball you can blow up the moon with no affects on the planet. I'm willing to bet that if you did that in DC, it would affect the planet.
That is just a couple differences between each universe's laws.
EDIT: Just like when some energy absorber goes against someone from another universe. Just because that random energy absorber can absorb all sorts of energy in his universe, does not mean he can do it another universe.