>Now how bulletproof it is in practice will be tested in years to come

Zero chance the data stays in the EU. Just think about it for a moment. US CLOUD Act directly conflicts with EUs GDPR. Amazon doesn't want to risk losing EU markets but it can't lose the US market by not complying with US law.

If these two conflict Amazon will side with the US. The savvy business move is to pretend to serve the EU market exclusively while privately adhering to the US demands.