Some of the best flights I've had are EWR
on 757s, 737-800s.
" commonly spend 6+ hrs in a narrow body."
is about 5 1/2 hours, this Summer I flew EWR
on a CO
757 and made it there (the pilot mentioned favorable winds) in about 5 hours (perhaps 5-10 minutes short of 5 hours!).
's 737-800s, 737-900s and 757s feature the mid-cabin lavatories, the 757 is really perfectly suited for trans-Cons. The 737NG and A320s are also suited for trans-cons to smaller markets, Long Beach, San Diego, Orange County etc..
Also keep in mind , when you compare a 5-6 hour flight from the US East Coast-West coast consider the huge amount of competition and routings/connections available.
Where in Europe they do not have that much competition on long routes, plus they are still funneling passengers through hubs like FRA
etc to get to place like North Africa.
In the US you can fly from Charlotte NC
to San Francisco, or Hartford to Las Vegas.
Apples and Oranges, the European airlines are about 10 years (or more) behind US Carriers due to their later de-regulation experiece.