I don't think that the difference in the size of the playing population matters all that much. There are still likely only a few who stand out above the rest of the 50,000.
The United States Chess Federation and FIDE never had a playing membership base of millions. Somehow, they were able to sort out the best players. The role of "Grandmaster" was established before there were even rating systems.
When online chess came along, millions of people received ratings. However, the very top of the pyramid remained quite small. That's partly owed to the pandemic and partly to a system that makes it difficult and expensive to achieve the over the board titles. Still, the main thing is that the decline in chess skill from the very top going down by a hundred points at a time is apparent. Ratings generally work pretty well.
I don't know what the right number is but if Game X has only a very small number of "Grandmasters", it might be reasonable-- perhaps a few dozen. If the number is in the hundreds, it seems likely that it's not the same thing at all.
When comparing ELO rankings in chess to ELO rankings in other games, should the n-size of players in each game affect the comparison? Asking for a friend [who might actually be reading this right now; hi, Lance].
I ask because Game X has an active player base of roughly 50,000, and my argument is that a GM in Game X can't be equated to a GM in chess because, at the very least, the player bases of each game differ by literal orders of magnitude.
Thoughts? Need your goodest brains.