Unfortunately the pluign documentation is a bit short and should cover more use cases. One of them is the assignment of a default label and, in case all hosts with that label are busy, a fallback label so that the job only has to wait if all hosts with both labels are busy. This would allow to specify a preference for faster hosts and fall back to slower ones if all fast hosts are busy.
Here's what I've tried so far:
But this always returns "SlowHost", no matter how many executors are free on "FastHost" hosts.