This is literally what happens all the time for all Internet users though wires and fiber on ground-based internet at similar or worse single-hop latencies.

The number of domains is irrelevant since most of those requests would be asynchronous. What matters is the number of hops that the traffic needs to take and the latency for each hop.

1.9ms times any reasonable number of hops would still produce a sub-100ms latency which is the FCC sites as their requirement, and would be a perfectly serviceable latency for nearly all Internet use (and is around what most users experience now).

It is unclear why the FCC would reference "the laws of physics" as a barrier for StarLink achieving this, as it is unclear how they would be causing any problems.