I think the problem with the quote is even more fundamental, because it's basically doing the D&D "some beings are just ontologically evil" thing with the later-D&D "complexity" of "but what if there are, sometimes, exceptions who overcome their tainted blood to become ontologically good" in a way that also effectively absolves Paarthurnax of guilt for his own crimes by just going "lmao, just dragon nature, nothing I could do you see, had to really work my way up to neutral from ontologically evil you know!"

It's also shitty writing because it dodges the question of guilt altogether: the argument becomes about some sort of internal being-good-and-thinking-good vs being-bad-and-thinking-bad dichotomy instead of the material effects of his actions and the factions he materially aided or opposed. As part of the hegemonic dragon empire Paarthurnax would have done monstrous things, fought to maintain an ontologically evil system, and personally benefited considerably from that system, and the only question is whether switching sides at the end and then entering a self-imposed exile is enough to redeem him and absolve him of guilt.

Also he's still a monarchist after all that time and thus is still ontologically evil anyways, so he's not even good he's just worked his way up from "literally eats people" to "at least tacitly supports a system that figuratively eats people."