Losing lp gains on winstreak again

This time it's 21, 21, 20, 19... I feel like next game I get 18 and land at 99lp (3 tiers in a row btw). I'm on a 9 game winstreak and my MMR is only just in the tier above, over 75% w/r on my main champ. I get Gold 2 jgl on my team that feeds vs plat 4 jgl, still win. Plat 2 Fizz player vs Plat 4 Zed on my team STILL WIN AND MY LP GAINS LOWER?! XD

This system is so odd, I'm clearly climbing really fast rn and the game isn't giving me MMR fast enough so I tend to win games, meaning games I'm in aren't competitive for anyone