Ranked Promotion

A little back story... I came back from a season 1 hiatus, and quickly jumped into Ranked. Terrible thing to do, I know. I thought I was way better than I was, i wasn't sure of the meta at that point and I was blatantly just bad at the game. I somehow was placed as S3 and lost my way to S5, before I started my self improvement.

Now I feel I play way better than where I'm at, however I do know I cant win all games, I'm a little baffled by the promotion system. So I worked my way up to 100 points a couple times, just to lose my promotional series. I've noticed that during that promotional series you lose LP, however I have finally got over my series losing streak and won it, just to notice you don't gain LP. I won the two games leaving me at 0 LP in my next series. SO basically, you can do all this hard work, just to lose your next game, as we cant win them all, just to have to do your series all over again?

Or am I just not seeing something here. Seems like they do everything to slow down your climb, but enhance your decent.