EASA rubber stamping the FAA’s rubber stamping of Boeing is still EASA making a mistake just as much as it’s the FAA’s mistake. This has become a major public issue, bet the problems started when the aircraft entered service.
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.
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.
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