As far as solutions to the quitting problem go, JiP isn't a very good one. I don't think it's as bad as some make it out to be, but there's much better answers.
JiP's problem is that in a sense, it encourages quitting, since you know that your leaving will have minimal impact on the match. It's also rough on people who join late and end up in untenable positions.
I prefer quit penalties. A solution I've seen in some MOBAs is to not let you start a match until the one you left is finished, with the option to rejoin. For people who have to quit due to circumstances IRL, it's not a problem, and people who quit needlessly or because they don't want to screw up their KDA are kept out of matches as much as possible. Other punishments involving ranks and stats are a possibility as well, but I prefer the elegance of the first option.