Okay, I figured out the problem. The problem was, I was over-thinking things, and didn't understand how #GDevelop multiplayer happens. Or how any multiplayer happens ever, really.
Basically, I was thinking about events as being run "server-side" and having to have loops and whiles to address all the players, when I really needed to be thinking about everything happening "client-side." There's nothing really happening that isn't happening locally in the player's instance and being shared with the others in the lobby. So events run for all players unless you specify otherwise.
This screenshot is the same as the first one, only it actually works for any number of players and it uses one event with no loops or conditions.
Honestly, this makes things so much simpler for a novice like me.
#gamedev