Vegeta is (probably) talking about when they're in the same form when he says "Our powers are higher than his now." The Babidi spaceship stuff is weird because he acts like Gohan's hopeless against Dabura when he could, on paper, just turn SSJ2.
Yeah, after my last research into the topic, it's best to conclude that everyone assumes Gohan's full power is his Super Saiyan power. How to explain the Budokai would probably have to go that Gohan got mad enough to transform, but no one expects Gohan to have that as his regular capable form.
Goku should really be telling Gohan to transform like he did at the Budokai, which would be much easier than releasing all of his rage.
It's just poorly written. AT's usual style is all about one-upmanship, greatly escalating things, powers, transformations, immediately and making yesterday's big thing, today's trash.
He attempts to do this by making Super Saiyan 2 the norm, but backtracks on Badibi's ship and wants to make Super Saiyan the norm again, to make Super Saiyan 2 feel more impactful.
He boxed himself into a corner and tries to pretend it never happened, meanwhile, the Super Saiyan 2 at the Budokai cannot be retconned as the power is necessary to ressurect Buu.
What he needs is some way to explain this and a changing of some of the terminology.
Goku and Gohan shouldn't be addressing what a fully enraged Gohan's power would look like, they should be talking about Super Saiyan 2 in general. But Gohan's Super Saiyan 2 seems to be directly attached to his rage post Budokai in GT and Super as well. It's more like Gohan has a "special" Super Saiyan 2 that taps into his dormant power.
This also fails miserably as well. This is even more egregious than the Piccolo issue which clearly showed him to be somewhat of a rival to the Super Saiyans at the Cell Game.
It's tough because the Buu Saga clearly needs to be rewritten for powerscaling purposes, but it'd be very hard to do so.
Also, he seemed to have changed his mind about how strong the boys were, on one hand, they were rivaling the adults, then later, can be easily one shot without worry.
I think he needed a lot more time, and less stress to figure out how to go about this saga properly, but he saw the end goal and just made it out of there as fast as he could. We still got some major classics out of it, Majin Vegeta, Ssj3 Goku, Fusion and so on were really cool concepts.