[phil21]

Load factors (both directions) are about as high as they ever have been.

In general terms, you can't really have a direction imbalance - especially due to the reasons you are positing. The vast majority of people flying (either direction) is on a tourist visa. Those people have to return as well as get there, so if a flight is full headed to Europe pretty much the same number of people must return. And vice versa.

Immigration/long-term business stays/etc. are a tiny fraction of the folks on the airplane. I suppose there could be an epidemic of US tourists overstaying their EU visas but I kind of doubt it :)

You'd see a reduction in load factor in both directions if there is a dropoff of EU tourism.