Yeah, goku and fat buu are a lot closer in power than kid buu and mr buu. Neither goku or buu was trying their hardest. Where as Mr buu was putting forth tremendous effort and had regeneration, and kid buu was treating him like a toy.
Blocking someone attacks causally with just your legs. As seen with Good Boo vs Pure Boo, the good one was losing power and regenerating after almost every attack. With Goku vs Fat Boo, neither were trying nor getting hurt.
Tanking seems to be the ultimate show of difference of power in DB/Z. Stuff like SSJ Goku taking a beam from Freeza to the face and then looking forward again without caring. The other side of the coin is showing a difference in power by having one side completely unable to take the hit....for example Gohan vs the Cell Jrs.
The top evasion feats would be making the other person miss entirely rather than blocking/parrying. Like Pui Pui vs Vegeta.
edit: in all 3 cases - certainly the SSJ transformations - Toriyama was trying to show a gulf in power. Having a fighter block the other wasnt so uncommon between close BP fighters, so is not used to show a huge gulf in power.