for resilience against the bluesky org turning bad I think its a better metric how easy it is to switch away from bluesky-powered infra in case you want to, than measuring how many people have done so while bluesky org is (still?) not bad
So yeah there are 1k+ PDSes, and you can switch from a bluesky-operated PDS to another operator, but that requires some technical skill and is not a 1-button click currently. So counting PDS numbers doesnt really show that