Some of the ranking is a bit questionable, but it is mainly meant for in-app selection.
As pointed out on different channels by various people, the issue here is the maintenance burden of such lists. If it’s not automated it’s quickly going to be out-of-date (and it has been the case already for some servers at the time of publication). It may be a goal of their but it’s just not there yet, not sure. Not everything is automatable also. I guess operators can join the effort of updating it if they’re interested in it.
I think diversity in this kind of list is necessary. There is no universal solution, there can’t be a single set of criteria. I wish for JoinJabber to get its own list at some point (that I don’t think should be exposed to users though, as opposed to this one).
Extensible Messaging and Presence Protocol (XMPP) is a communication protocol for message-oriented middleware based on XML. Learn more about it here.
Dedicated Lemmy instance
XMPP.net Provider List
Also see JoinJabber.org FAQ