Exactly, my point is that the design of Sekiro is so fundamentally unforgiving that giving you a stats advantage wouldn’t make the final fights substantially easier

I don't agree with this. Fundamentally being able to tank more hits, being able to make more mistakes would make it easier.

letting you get there without properly learning from the content beforehand would be like trying to teach a child factorials before you’ve ensured they properly understand addition and multiplication.

You're misunderstanding, someone can know how to do it entirely, that doesn't mean they can input reliably enough to not make mistakes.

In this very thread, there’s a comment from a person playing Sekiro with a mod to scale the game down substantially who’s still finding the game prohibitively difficult.

That's not what their comment said. They said they're still finding it difficult, and imply it would be prohibitive if it weren't for the mod. So yea the stat scaling is working for them.