It surely does convey the intention quite well, but not trying to send diffs in the first place is probably the better implementation than trying to send them just to discard them on their way. I’m not sure how performance intensive a noop intercept is, but it has a warning that customizing messages per user can become a performance issue.

If you track users in presence using e.g. something like an internal:users topic I feel like the intend can be communicated in a similarly explicit fashion.

cool! thx!

I had another method found earlier within this forum and that is to
intercept(["presence_diff"]) inside the channel module. That’s the message phoenix tries to send to provide the presence to connected clients. By intercepting you are able the change the outgoing message (even changing it to a no-op and effectively not sending a message to the clients).
To change the presence_diff message you use the following in the same channel module (where you just added the intercept line from above):

def handle_out("presence_diff", _, socket), do: {:noreply, socket}

Because this function returns a noreply it will not send out any presence information to the connected clients.
I guess both methods work but maybe this method conveys your intention a little better.