Shin makes assumptions about the strength of Badibi's warriors. "Badibi only collects the strongest warriors in existence..."
And they are very powerful. We're already giving him a lot of credit by placing him above Kaioshin, but back then Freeza was the absolute strongest in the universe, so I understand people who place him below Freeza. Yakon is from the demon realm though, so he's easily above Freeza.
Anyway I don't really disagree with you here, I just think it you need that much room to make it work. Shin though Saiyans were stronger than him but he knew about SSJ. When he forgot, he thought they were weaker than him. If he hadn't forgotten, I'm sure he'd have been alright the whole time.
Babidi and Dabra are expecting people weaker than Raditz. Look at all the evidence: Dabra basing his estimations on 300 years ago (Mutaito's era), they think SSJ2 Gohan's energy was a bunch of normal people. And in Babidi's head, surely he'd have heard of and recruited some Earthlings were they that strong? Stronger than the Supreme Kai?
Hmm, I wonder if I have been neglecting Goku's advantage over Vegeta too much. I think I have been.
There's really no reason for Vegeta to have closed the gap on Goku at all, the gap should be just as massive as it was during the Cell Games. Since Vegeta says, "I couldn't close the gap." Now, this doesn't have to be taken so literal, but, I think it should be. The idea that they gained equal power alongside each other sounds right. But Goku is just always one step ahead. I think this is the best way especially to make other key things like up.
This allows for Kid Gohan to have a significant rage boost, which seems likely as well instead of the typical 1.2x I am forced to give. It allows the CG powers to pale in comparison to the Buu Saga powers as it feels.
It's possible, but I'm running with the 2x multiplier and running with SSJ Goku being close to SSJ2 Vegeta sounds nasty. If the multiplier was 4-5x SSJ1, I surely would keep the 1.5x gap.