There's a couple things I don't like about the LP system.
I'm not gonna make a huge thread ranting about it. But I'll give a couple statistics.
You can climb to your promos with a 51% winrate.
You can't win your promos unless you have a 66% winrate.
The way the promos are created, you have to get a ridiculously high winrate for 3 games in a row with randomly matched teammates that can do and act however they want, whether it be trolling, afk'ing or trying to help.
Additionally, I don't think promos should deduct lp. It puts too much reliance on the 2nd game of your promos. If you go on a winning streak and get to 100 Lp, and win the first game, then lose the second, you'll lose 20-30 LP because your MMR isn't as high as what rank you're playing at. Putting you at 70-60 lp if you lose the second and third game of your promos.
Whereas if you lose the first, win the second, and lose the third. You suffer a slightly smaller deduction of LP (and I mean like 2 or 3 lp difference). Though it's still there, and it's impactful. 2 or 3 lp is the difference between 97 lp and 100 lp.
TL;DR: The LP system and promos system create too much of a grind; you need an absurdly high winrate to climb now.