This announcement from Bravo caught my eye and looks like a step in the right direction:
> As promised, the Majestic FFA DLC playlist has also been updated – Rumble Pro has been corrected to have the motion tracker enabled, and the join-in-progress window has been shortened to prevent players from joining games too late. We have also updated this window for the Regicide and Team Throwdown playlists. While Team Throwdown was originally slated to not include join-in-progress, we have noticed that games have been starting with lopsided teams due to players backing out of lobbies, and we have included a very brief window before and during the first few moments of a match in which Matchmaking will fill and balance teams. We will continue to monitor this window to ensure the best Matchmaking experience possible.