This seems not fully worked out. Assuming total travel is constrained, selectively limiting travel to particular areas concentrates travel in the remaining areas, which increases the average number of contacts between travelers, which violates your “reducing exposure to other people is best” rule of thumb.
By your model, some reductions in travel ought to have a negative effect. Is that a fair corollary?
There’s no such thing as a fixed amount of travel, and constraining it on one way concentrates it in another. That makes no sense. Constraining travel will reduce travel, which will reduce interactions between people, which will reduce the spread of the virus. We know this empirically from previous outbreaks and countermeasures.
The pressure / desire to travel is also dropping sharply, though.
Limiting all Schengen traffic is an extreme example, but it's not obvious that some level of restriction would necessarily produce a significant bottleneck effect (given that citizens are exempt).
Why would you assume total travel is constrained? Restricting travel from Europe to US will just eliminate that portion of travel, not concentrate it in the US.
By your model, some reductions in travel ought to have a negative effect. Is that a fair corollary?