I think we're exaggerating casuals a bit too much here. And there's really what seems to be three levels here instead of two: enthusiasts, casuals and basics.
The enthusiasts invest more time and effort in what they do in a variety of ways. The lore is deeply known by them, and can easily be referenced by them off-hand. They take RP matters and order more seriously.
Casuals tend know enough of the lore to establish their characters to fit into the village system and RP system we go by. If they need help though, they tend to ask enthusiasts on a few matters here and there.
Basics are just that. They know what RP is, but usually like to be quick and short about it. Some even go their own way, and establish themselves as someone just as ancient and powerful as Hagoromo, sometimes even more powerful just because they have the liberty to do so with text.
Back to the topic on-hand, I don't think creating a whole separate list would play out very well. Maybe if a Tailed Beast is literally split in RP into Yin and Yang halves, that would be a different story. But even that would still be something noted on the current list.
Anybody could say they're the Sage of Six Paths or Kaguya Otsutsuki herself. Or perhaps of immediate family to some canon character, even if there's already someone playing with mentioned canon character and has never interacted with that player. Or even mention an event or canon character's actions in the series, but one that never occurred in SL's history itself. Maybe they happen to be of high rank or authority in a certain village, while never interacting with said village's members or kage.
Point is, casuals aren't the problem here. Basics aren't really causing a problem either in this situation, as both enthusiasts and casuals usually see their claims to not be in line with the mainstream RP. A Tailed Beast is certainly a responsibility that not everyone can handle, and is usually in the hands of someone who is not only active, but also a cut above the rest in RP in general. Not everyone will end up as equals in terms of position and power. There has and always will be less people at the top. Though the bottom isn't an area where people are starving and dying in terms of RP. (Maybe if you want to write your character like that for the sake of RP, it's still your choice to have them go through that.)
I do think everyone can get to resolving things, though not everyone really wants to in the same way. But that's always been a core mechanic of conflict.