Haven’t read most of your post but:
This has no relevance to a steelmanned Popper that focuses on his key critiques of induction and a stripped down solution (conjectures and refutations and error correction and evolution) that omits corroboration which isn’t central or really necessary. Corroboration is an attempt to add more detail and solve additional problems, but it’s not required to decide induction is wrong and have a general framework for an alternative.
Also the question isn’t devastating at all. The more effort we put into error correcting ideas, the better those ideas are on average. Everything else being equal, they’re lower risk than new ideas or ideas that got less critical review. Even if abstract epistemology theory ought to go in some other direction, there’s a straightforward and fairly reasonable and practical answer to this question.