At the risk of being slightly off-topic, when looking at the phrase "for better maintainability and performance with GitHub Pages' CDN and future-proofing in case we wanted to switch to a different platform down the road", I do not see a compelling reason for the work expenditure. Unsurprisingly, in solving problems they didn't actually have, they managed to create an entirely new set of problems that they wouldn't have otherwise had. (And the problems they created look to have teeth to boot.) To me, the lesson here is not about SEO, it's about effective management.
