Plat+ LP gains and losses are still an issue
It makes you feel like you're in a casino since if you play many casino games, the house will always win, while most video games design their systems so that if a player plays a lot of games, the player will slowly win over a long period of time. In fact, I think LP gains and losses are even worse than the odds of most casino games (Roulette, for example, gives you a 95% return on your bet, blackjack gives 98%). In plat right now, I gain 40 per 1st and lose 60 per 8th, and that factor is the same for other placements (aka I lose 1.5x more for a loss of 5,6,7,8th place than I gain for 4,3,2,1st). I typically gain +28 for 2nd, +18 3rd, +6 4th, -9 5th, -25 6th, -40 7th. Assuming that I have a 12.5% chance of placing in each of the ranks (aka supposedly breaking even if LP gains were fair), that means that I can expect to lose about 5 LP per game. This may be mitigated by things like an 8th place only demoting you to 75 LP instead of losing the full 60, but as someone who wishes to actually climb to diamond rather than just drop slower, it's not much of a consolation.
These LP gains are the LP gains that a plat player should get for playing with silvers, not other plat.
I don't think my MMR has an issue. I play mostly with plats of my own rank, and many other plat+ players, including top streamers, have the same issue so I doubt that it's all of us having bad MMRs.
I have to say that LP gains have gotten better since 9.15 (back then it was +37 for 1st, -80 for last), but better still isn't equal.
TLDR video games aren't casinos. Video game progression should either be net-zero or even slightly benefit the player, not the house.