If you think just a bit about it, SSJ Vegetto = SSJ4 Goku doesn’t make any sense.
Golden Oozaru is obviously 10x SSJ3, and Goku was on SBV2’s level after that. In turn, SBV2 going Golden Oozaru put him on par with SSJ4 Goku. That means SSJ4 is 100x SSJ3, more or less.
That also means Base Vegetto is stronger than GT SSJ3 Goku. Base Vegetto is at best = Majin Boo. Base Goku is stronger than Majin Boo, but SSJ3 Goku is weaker?
This also applies to @SSJ2’s scan. Base Goku > Boohan means SSJ3 Goku alone blows Super Fraudetto out of the water. Baby is just saying he’s the strongest now. This isn’t a reference to a character who’s not even mentioned in all on GT.
You're on the right track but remember that GT follows the original anime as its canon, which should include all the had powerups. Base Vegetto is stronger than Buuhan in the anime.
With Kid Buu as the strongest Buu, Goku should likely match that power in base along with Uub by the beginning of GT.
Here's the problem: Even if(as a lowball) doesn't power up in base between the start of GT and when he gets SSJ4, with SSJ4 being 100x SSJ3, if SSJ Vegetto rivals that, then by dividing by 50 that puts base Vegetto at or over 800x Kid Buu, and thus even higher than that over Buuhan. If you need Vegetto to his SSJ3 is a rival to baby saga SsJ4 Goku, that only cuts it down to 100x
I think it stretches believability that Vegetto would be that much stronger than Buuhan and even bother to use SSJ at all. I think it fits better to be about relative powers rather than absolute powers.