Well, according to that theory all servers are fungible, but having read over quite a few of the Mastodon /about pages over the past few days, they are for sure not. The audience and sometimes the rules vary wildly

Also, while yes federated etc etc, I for sure get a lot more enjoyment from the "Local Timeline" in my server than trying to keep up with the absolute firehose of "Federated Timeline" which is another reason to pick one where the local content would be interesting