This is quite good even by European standards. If you were paid 4.5 months because the law said so then it isn't harmonized, because in my EU country it is only 3 months notice afaik.

Also not sure if the Meta severance applies to contractors as well, but many engineers work as contractors by which they of course opt out of worker protections.

It's not the same as workers protection law is an EU directive so each country implemented it on its own.

yes but having both the sky-high US salaries AND termination conditions similar to Europe is kind of a win-win

Only for sky-high earners. Are low paid keyworkers getting same benefits or becoming homeless?

What are you talking about and in what country?