Intentional quitting for nothing other than the fact they can't dominate an enemy team is a pathetic practice IMO.
It means that their stats really dont reflect them having any skill at all, just that they are cheap asses that quit as soon as they dont have the upper hand with the ability to just stomp another whole team with ease.
I think after a few intentional quits having a timed ban would be fair, but there's no way to accurately ascertain why they have quit/dropped out.
If it's only placed on quits from the in-game menu, I can see these people just dashboarding to circumvent the counter and avoid timed bans.
If it applies to all disconnections, it will punish people with messed up internet connections or people just trying to sort out internet issues as well as the intended targets.
I don't think there's really an effective way to do this without punishing some undeserving people in the process, while still making it robust enough to not be circumvented with ease.
Perhaps a better solution would be to give incentives for staying for consecutive rounds as opposed to punishing for leaving, such as maybe slightly increasing glimmer amounts (or something like that) each round, similar to F2P games with the daily login bonuses. Not a massive reward, just a little incentive to keep you in game. Or, it could just be giving you an engram every 5 or 10 consecutive full rounds you play, or something similar and resetting the counter to 0 when you quit mid-round.
Rewards for staying would be more effective than punishing for leaving I think. Might make people think twice before they just quit because they aren't going so well =)