I wonder if you could optimize for reducing the total probe count (at the expense of possibly longer total time, though it may be faster in some cases) by using some sort of "gradient descent".

Start by doing the multi-continent probe, say 3x each. Drop the longest time probes, add probes near the shortest time, and probe once. Repeat this pattern of probe, assess, drop and add closer to the target.

You accumulate all data in your orchestrator, so in theory you don't need to deliberately issue multiple probes each round (except for the first) to get statistical power. I would expect this to "chase" the real location continuously instead of 5 discrete phases.

I just watched the Veritasium video on potentials and vector fields - the latency is a scalar potential field of sorts, and you could use it to derive a latency gradient.