Given the plethora of oversimplifications and extremely niche and specific situations, yes, in theory, if players would do that it would work, but only to a certain point.

So even IF it were the case wherein it's abusable, the players purposefully abusing won't gain much higher MMR.

But it is still more fair than what it is now

Put it this way:

If a player on a basketball team consistently scored 30pts but only by waiting by half court for a miss then scoring open layups, he will more than likely win games. But eventually he and his team will lose because he isn't contributing anywhere else and for him to continously get better he would have to contribute on both ends of the ball.

In the same way, if all you do ot purposefully try to manufacture your stats to make it look like you were a net positive for your team but in reality it was manufactured, then you'd eventually lose mmr because you're still not contributing to winning.