4v5 4v5
Make the AFK/leaver take all the MMR loss. Game didn’t count for his team mates that actually played.
Just talking hot join here, tPvP is a different animal.
It doesn’t make any sense to punish someone for leaving. I know this is hard for some folks to understand but real life matters tend to trump gaming matters. It would make more sense to punish someone for creating a mismatch like joining a 4v4 in progress and making it 4v5. However, it would be heavy handed to do so since, ultimately, a 5v5 match is ideal and waiting for another person so you can synchronously join teams is a bit clunky and not realistic.
If the engine was designed so it would queue players to introduce one on each side at a given time, that would work much better. Unfortunately, it would still leave the door open for a player to leave and create a mismatch that way.
The bottom line here is that hot join is designed for casuals to jump in and out and make the most of short periods of game play time. If you can grasp that, maybe you can grasp that it doesn’t need to be taken too seriously and win/loss is basically arbitrary.