[throwaway5752]

It's nowhere near as big of a mistake on the EASA's part. You don't understand how international regulatory and standards bodies interact with each other.

There are explicit agreements between the EASA and FAA in order to reduce duplicated work (https://www.faa.gov/news/updates/?newsId=88965)

This is extremely bad. It it will be bad for any US regulated product used in EU markets like food, medical devices and equipment, pharmaceuticals, among others.

[Retric]

These agreements don’t require EASA to accept everything FAA does.

From your link: each entity performs a “validation” of certification activities.

[throwaway5752]

Do you know what validation means in that context? Not to be glib, but "validation" and "verification" and "certification" are not common language in those contexts and have fairly precise meanings. It does not mean they will perform the test again, and in practice probably means they will review the activities in the certification with the assumption that "qualified persons" planned and conducted it. Essentially, an agreement that the FAA was competent and trustworthy with minimal checks to ensure that was the case. That has actually been historically very reasonable and sensible, and this is a rebuke to the FAA from the EASA. It will raise costs and time for US airframes to get to EU markets, which essentially means globally.

edit: not precisely my area of expertise, so corrections welcomed