How is this still a thing in competitive? The whole concept of “It will be abused” is an absolutely pointless argument when it comes down to actually looking at how that would be “abused”.
If you have a group of 6 friends and they all think they will ‘abuse’ this system by leaving… first of all- the person who leaves, gets hit with a 100 SR hit, which I think is fair. Then lets say in the most lenient (fair) system, the other 5 get no SR lose and the ‘winning’ team get half the normal SR gains.
Now if someone wants to abuse this, not only will they need to have multiple smurf accounts at nearly the same level, they will have to be content with burning that 100SR and dealing with an eventual competitive ban for leaving games so frequently. So they will what? Purchase another account, grind to level 25 and do it all over again? The time that this process would take is absolutely insane to have any meaningful impact. Not to mention most ‘win rates’ are like 70% at BEST, so you’re going to lose fairly frequently.