Hello,
if it was up to me, I would not create this setting, but I would actually completely disable reconnection/disconnection notifications, but only in the main room. As it is well said here, in English there can be over 50 people here, and reconnections are quite frequent. On the other hand there's no chat in the English main room, so it isn't all that useful in practice to hear such notifications. Sure, you might be privately talking to someone who is in the main room at the moment, but that's more of a lucky case...
If we do that, we can restore the reconnection/disconnection messages to the table messages channel, and thus have them back in the discussion view, I'll talk about the history of that a little later down below, but basically the only reason I have the global messages channel enabled to speak at the moment is to hear if somebody disconnected.
As for the setting to be notified about friends only, I don't think this is so useful. It can be very useful to know, OK, my friend/favourite created a table, I may join them. However, for reconnections/disconnections, I don't really care if I am playing a game or talking with my friend or some random person, it is still useful to know they went away, so I think this should always remain global.
About the views and channels: In 2021, it was suggested to have reconnection messages under the discussion channel.
It doesn't say this anywhere here, but this was actually accepted and implemented, and these messages went to table messages instead of global. However, after the April 2022 update, there were many connection issues and people started to complain about constantly hearing that someone reconnected while in the main room (since table messages really shouldn't ever be disabled), so this was reverted back to global messages. I think these complaints are legitimate, hence why I said, my preferred solution is to kill these notifications in the main room, not to move the messages back to global messages.
That being said, I am not sure if it's worth it. Sometimes the disconnection notifications are very reliable, but very often they are completely inaccurate and you really shouldn't rely on them. My experience suggests you always get the notification if someone reconnects, but not so often if a disconnection actually occurs. Most often you get the disconnection notification only many minutes later, when they're about to be kicked from the Playroom due to being disconnected. Probably the best idea is to repeat your message if you find it ignored/missed, even though that's of course not the ideal solution.
I'm not sure if it's possible to do something here and try to detect if someone's client is no longer responding and output the disconnection message faster, but it would actually be quite useful.