Who are these "misguided practitioners" of Buddhism? Are they just the authorities you disagree with? Can you name an authority who agrees with you about nirvana? I'm sure I can find authorities who say the opposite. So there's disagreement on the manner, which is fine and to be expected. There's no need for the ad hominem attacks when the issue is just that you disagree with some prevalent ideas about Buddhism.

The tangled knot of personhood is the mind that's based in the tangled knot of the brain and that unfolds into cultural complexities and feedback loops.

You're asking me whether severely mentally challenged humans are people? If they have mostly functioning human brains, it's a safe bet they have some personal inner life even if their expressions of it are limited.

For me, the key ingredient of personhood is the intelligent, creative experience of the existential predicament for living things that find themselves in an impersonal universe. Some deal with that authentically, and most deal with it inauthentically. But both reactions are signs of personhood since the latter betrays an unconscious recognition of the problem, whereas many animals might be ignorant of the problem's universality (because they lack the relevant concepts and ambitions).