Clearly you have no clue about Norwegian or the route structure of different airlines.
"US to other destinations that doesn't originate from their flag of operation"? Come on, you think this is new?
How about CX YVR-JFK?
QF JFK-LAX?
SQ ICN-SFO?
Or how about DL JNB-DKR?
There's nothing shotty about their mx, and their pilots aren't poorly trained. EASA ATPL is _WAY_ more difficult than any FAA certificate.
Before blindly repeating some ALPA propaganda, I recommend researching it yourself. You would not be qualified to fly for Norwegian in Europe, the requirements and standards are too high, but you would qualify for their planned US operation because they use FAA standards for that which are lower. Their recruiment process is more like Delta/American process, not like US regionals where if you have a pulse => job offer.
Being based in Ireland is corporate tax strategy, it has nothing to do with pilot training/standards. If something is a safety concern, it's the Asian "ICAO level 4" pilots who don't have to declare emergency, because ATC already has cleared the airspace for them...