For KH theory. I think KHUX era is the time when the keyblade wielder were strongest. There were more people and more activity, so there were many techniques, spells and tools created specifically for keyblade wielder . But in DR era and so on, most of those were lost so they become less stronger. It's also integrated to gameplay system where KHUX got ridiculous amounts of level and taking on booses easily.
I can definitely get behind that interpretation of the setting in DR. Basically the effects of the fall of Daybreak Town just obliterated the Keyblade culture and any sort of power they could taut. I mean, the Foretellers from Back Cover have some pretty insanely powerful abilities (I’m looking at some of that dimension cutting jazz, like chill out) and they are easily the display of peak Wielder. We know the Union Leaders are strong but there’s nothing like losing an entire civilization’s worth of knowledge and abilities. Brain doesn’t have the time or skill to propagate the prime Keyblade knowledge on his own but thats what he was (presumably) forced to do. That being said, I think Scala on its own is still a marvel and we are meant to get the impression that the surviving Keyblade Wielders built something great (or potentially greater) than the humble Daybreak Town. It’s still very incredible that they rebuilt the society into Scala. It’s potentially a front because as you said, the gameplay of DR suggests that they’ve been nerfed. It’s confused by how Xehanort speaks highly of Scala, making it seem like that was a level to aspire towards and I guess compared to the current population it is. But we’ve seen something even greater in the Keykids of Daybreak Town and the Masters before them.
