If you were to ask my opinion of it,
it's not, it's just an arbitrary comparison. I mean, I don't remember the exact thread but I'm pretty sure the head honchos who revised the tiering system just decided the hierarchical transcendence would be the same as baseline High 1-A or (inaccessible cardinals) when Donttalk requested clarification on the matter.
There are a lot of arbitrary comparisons we use for these kind of high tier verses, like reality>fiction interaction being the same as uncountable infinity required for the formulation of higher coordinate spaces or that countably infinite dimensions exist, when they must by their very nature be uncountable infinite.
It's just something to make classification easier, it's not really an accurate portrayal. Personally speaking, the gap between 1-A is >every tier that came before so hierarchies should technically be meaningless at that point.