the amount you lose/ gain is based on your MMR; if the game thinks you belong in bronze 1 and your in silver 4.. you're going to lose a a LOT of LP and gain very little until you convince the game you belong where you are. (aka your raise your MMR to your current elo or higher)
idk exactly what it takes to make the game think your are where you belong.
if it is only win/loss, then i don't see why there is a point to even having MMR. So i assume it takes into account how well YOU did, and if YOU are the reason you won or lost..
or at least that is what i would hope.. but i really don't know exactly what affects MMR.
i am pretty sure it take into account your teammates MMR and whether or not they are in a pre-made and adjusts how much MMR you win or lose if you win/ lose the game. but i really don't know if it looks it how well you yourself did that game.
i just know that if you MMR is at a lower elo than your current elo you will lose more and gain less. and if your MMR is at a higher elo you will gain more and lose less.
and although it has never happened to me.. if your MMR is WAY above your current elo you can skip divisions...