Hey there.
It’s unfortunate but /who is a bit wonky and not always accurate.
However, some Era servers have dips in population depending on the hour or day. Some servers are heavier on one faction than the other. There have been server connections and Winterly listed servers included in the Whitemane cluster.
This shows the transfer destinations and how the attempt has been made to consolidate populations. There’s no accurate site that I know of that can give you exact numbers. I have characters on a couple of servers but am not currently playing Era. One of the servers where I have characters is Bloodsail Buccaneers which is RP-PVE and not currently connected with any other realm. Horde players on that server will number in the single digits regularly. Hopefully someone will respond with a better idea of numbers elsewhere.