The US airlines overall treat their elite flyers better than the European ones do - in terms of benefits and awards. It is just the lounge product in the US which generally is of lessser quality than anywhere else.
The reason always given for that is the high load these lounges must accomodate. But that does not justify why an international F lounge in the US does not even match a domestic C lounge of an Asian or European carrier.

What you are perfectly right about is what concerns flying US domestic. I can get into the RCC lounge with my LH gold card but not with my UA one. This has some entertainment value .