First off, the penalty is a good idea if applied correctly. Leaving early and getting penalized is great, but what about the team that gets screwed over? There needs to be a Forfeit option or once someone willingly quits, it allows the others to leave with no penalty, even if someone session joins. That 30 or 40 seconds it can take to get a new teammate, screws up the entire match. You CANNOT play this game 3 on 4. So as soon as someone leaves, their remaining teammates are trashed by the opposing team, 9 times out of 10. There needs to be a solution to this because it ruins the whole game.
Also, add a selection option to the play mode. About 50% of the people who play this game, seem to want a Team Deathmatch mode and refuse to play the objective. I'm tired of my profile and stats getting trashed because the developers didn't add in a deathmatch mode. I'm sure most players would agree it would be nice to squad up with like-minded individuals who actually want to play whatever mode they picked.
Not easy or fast fixes I'm sure but these improvements will help the game grow and recruit more players.