Empirical evidence through observation or self-reporting, sampling in some meaningful way, would obviously be preferable but is also often just not practical.

Guessing at numbers to check whether your thesis even works with some plausible assumptions is a meaningful first step and to my mind a good way to reason through something like this and make it discussable.

A possible outcome of such an exercise is also that for your thesis to work out you need to make wildly implausible assumptions, so that helps you to discard that thesis.

From my perspective this is a very useful way to approach a hypothesis where empirical evidence is scarce or at least hard to get. No reason to dismiss it immediately – especially since the fact that those are guesses was never hidden.