I agree, it's always annoying when people quit in br. There was one pubs match where the two teammates quit that I went ahead and played and I know I could have won it if at least one of them stayed, but because one fight we took was too hard they left.
That said, the only match I quit in a long time was on wildcard. It was me, a random Caustic, and a real toxic player that kept swearing at me and the Caustic. The Caustic actually had a 4k badge and a 20 bomb badge on his profile and the guy swore at him telling him to go kill himself and do the world a favor and that he played so bad the only way he got those two badges had to be from just putting the gas out and getting unsuspecting people to run into it, which he called "lazy." (sounds like good strategy to me) Then, he told me I was garbage and should quit the game because I only had 2 kills and 200 damage up to that point and was making what he called "bot-like" mistakes. My headset mic was broke but I typed "This is a game, something people do to have fun" and I quit the match, since there's no reason to stay with a toxic player if it's going to upset you.
So, I'm kinda torn on this one. I think pubs needs the penalty since it is shorter matches anyway and even if you are about to die you should at least give your squadmates a chance to pull it out and revive you. However, I think the abandon penalty should be removed in Mixtape and LTMs since they are longer matches and have more cheaters and toxic players. Maybe if mixtape is able to put a replacement player in real quick from the que like it sometimes does people quitting wouldn't impact the matches that much, and same with LTMs like wildcard.