One can't view a question like this exclusive of the larger picture, but one also cannot study something without a necessary isolation. You are unable to view a specific question on a specific topic without injecting a "world view" or assuming an "agenda".
So instead of holding the legitimacy of the V2 usurpers in doubt, you'll cast doubt on principles that have been widely held and taught by the vast majority of theologians,
Incorrect. The legitimacy of the V2 popes ARE in doubt, for numerous reasons (potential Fɾҽҽmαsσɳɾყ ties, potential heresy, etc). Due to this doubt but also due to the doubt of their orthodoxy (which I consider a separate issue from their legitimacy), I also doubt their canonizations, but this is mostly due to the change and corruption of the process. Had they stuck with the same process, I'd have less doubts. I don't doubt the principles.
Cantarella will reply that "the process doesn't matter; what matters is the pope's declaration". No, the declaration only matters for "de fide" truths, because those are DIRECTLY connected with Revelation. Canonizations are indirectly and remotely connected, with the process, investigation AND MIRACLES being a necessary aspect of the declaration. So a corruption in the early steps, gives doubt to the final step.
And I'm allowed to have such doubts or questions, because of the lesser theological note which are attributed to this type of declaration. How can you say I doubt the principles, when I'm allowed to question the outcome?