There's no realistic way to measure performance and assign and win or loss based on it.
This is how team games function. The team with the highest score at the end wins.
You can crush in basketball, but if the enemy team has more points at the end, your individual performance simply wasn't good enough.
Now, having said that.
I do not like how the system tends to match people based on their MMR. If you have Plat MMR, but you're in low gold because you just finished placements, you shouldn't be going against teams matched to your skill rating. You should be matched against people based on your division. I don't think it's an accurate system where someone has to compete against people at their skill level regardless of their division. If there's a diamond in low gold, give him low golds to play against until he climbs to where he belongs.