One thing that is pretty apparent, regardless of laws or rules, is that senior US flight attendants are not as polite or courteous as those of foreign carriers. Sure they have experience, but they lose something in enthusiasm and attitude..
The foreign carriers are no homogenous group at all.
You get the truly friendly ones on NH, JL, OZ. The fake friendly ones on SQ. To the ones from TG who look very much as the UA staff at the plane as their personal property, down to the patronizing flock that populates BA's birds to the cannot-be-bothered personnel chez QF.
I am unconvinced that EU carriers generally have better staff than US legacies.