It's how it works in dota as well. If you abandon games because of something, even if you rejoined and help the team win the game you get literally nothing. You lose MMR and you still get leaver penalty.
I feel like at the very least you shouldn't get leaver penalty if you get leaver penalty, I'd argue you shouldn't even lose MMR if you win (but not gain mmr as well), but at the VERY LEAST you shouldn't get matchmaking ban.
Right now there's literally zero reason for me to be respectful to my team and reconnect to help them if I somehow got an abandon due to something out of my control