I still hate the MMR system

Let's try to put this into perspective with examples.

So, your MMR is pretty good. You've been doing well! Good job.

You're playing a tanky jungler. You work your heart out to get your ADC and Mid some kills. Good job. Your ADC and Mid are actual trash, and in every teamfight, you realise you've been going into 3v5's with your tanky support and mediocre Top laner, as your ADC and Mid spend their entire time either running away from the fights you initiate in or trying their hardest to run in front of you to become the new front line and die. So you lose.

So, your MMR is decent. Seems it got worse, though; I guess that must be all your fault for being the only bad player on your team.

You're playing an ADC this time because you want someone to do damage. Your Mid feeds again, your support turns the lane into a 1v2 which leaves you under-farmed and underfed, and your tanky jungler somehow misses all his abilities and becomes a mild obstacle that can be ignored. You become an easy target for the enemy divers, and no matter how hard you kite as an immobile ADC, you can never seem to fend off the 1v5.

So, your MMR is lower than average. You will continue to tank unless you improve your play!

Example over.

Is that exactly fair? Is there actually no better LP gain/loss system you could implement?