If you start a game you commit to it for its full length. If you are in doubt that you have enough time, play the quicker game mode instead. The system shouldn't account for emergencies since they are the exception, not the rule.
A surrender option would be great of course but it wouldn't solve your problem in most situations since there are enough people that just won't surrender no matter what, which still leaves you stuck in the match.
And that it doesn't matter is just flat out false. People's fun matters. In a game, fun is paramount.
You ruin it for others by leaving.
Harsh punishments make sense in this context.
I don't agree with the punishments when someone leaves during agent select though.