Look,
If a player quits a game they do so for various reasons. For example, I quit a mission, I already have a 9.0 on as a Raider because I was teamed up with 2 rank 6's and an unranked player. There's no way I was getting a better score and if an Antag joined, very probably a loss due to him/her targeting my teammates. Also mission difficulty would be very hard for them. I quit. Then it means my Guild Aequilibrium bonus drops as well. That was 25 minutes ago and they're still on the mission. Your 'cancel' button, when asked if you want to rejoin or not is broken. It puts you back in the game if you press it - game testers hello???
So, I'll get a 5 minute penalty, but making me wait until they finish the game is asinine! I could be helping others during this time.
**Edit**
After a 30 minute game end wait + penalty, my next game after a long wait is with another 3 rank 6's. Again an instant game quit before the game started. I've no desire of blundering through the Aneska mission, that'll likely take nearly 30 minutes to finish, if I finish. I have an MMR of 46. What does this mean? Your pool of players is dropping MSE.
***Another Edit***
In fact remove penalties altogether and allow players to drop into a game if they're missing players. You have no in-game player block mechanism, which won't team you up with said players. I'll instantly quit any game with a player I dislike. You have to give people the option to play or not to. Penalising them for refusing is draconian. I hate taunts and people who taunt me get blocked immediately.