Yea, that doesn't seem like that useful of a number, since Frankfurt is a fairly major layover airport for international travel.

I guess the more specific question would be how many Germans fly to elsewhere in Germany or Central Europe vs. taking a train. I generally have to either do a long car trip or a flight to get around in the US outside of some specific corridors. Presumably most of Europe has the option to take the train instead, but are they?

And yet layover flights are decreasing since the 2 engine restriction was "lifted". A 787 can fly non stop for as long as would be comfortable for someone to be on a plane.

According to Wendover Productions.

But there’s still a connection/hub-and-spoke system. You could fill a 787 with enough fuel to fly from Columbus, OH to Venice, but you couldn’t fill it with enough people to make it make sense.

And airlines usually charge more for direct flights (price discrimination), so for leasure long-haul travel it's fairly common for Europeans to have a flight with stopover, even if there's a direct connection available.

Also all international trips are irrelevant for comparison as the ICE traffic is national.

Give or take. There's plenty of trains between countries in Europe that would also be within driving distance.

In my mind, the optimal realistic situation is to have rail for longer distances (1-8 hours), but not trans-oceanic obviously, and then either ICE or local light rail for smaller trips

The relevant point is that there are no (or very few) international ICE trains. Cross-border are usually slower Euro-city trains that shouldn't be included in the ICE statistics.