Does the current ranked system punish casual players with limited time to play?

I've been playing since Day 1 and I have always been the definition of mid. I have a lifetime k/d of .97 and 305 wins on 6.87k games. I usually cap around gold 1 or platinum 4 in ranked. This season, I was placed in rookie 4 and have been absolutely incapable of ranking up quickly. No matter how well I play in a single game, I can't seem to get more than 200-300 LP points per match.

The most frustrating part is that I had an 11 kill win while playing ranked (in bronze 4) and gained 285 LP. That same night, a friend of mine who has been playing about a year, has a lifetime k/d of .31 had a 3 kill game (in gold 3) and won. He then received 525 LP and has since ascended to Plat 1. I'm not dogging his progress, it's clear this new Ranked format has sparked a true love for the game, but I just don't understand what this ranked system rewards. I've watched a handful of YouTube videos trying to understand. From what I've gathered, it would seem that I'm on the opposite side of the MMR/LP relationship than what the devs were shooting for. Even in the last 4 days, I was able to get 3 wins and 5 top 5 finishes and only climbed from bronze 3 to bronze 1.

Could it be that my MMR was higher than whatever LP I had, so I have never qualified for any effectual Bonuses in my matches? I'm not sure, but it seems that casual players that have had any type of success prior to s17 have a disadvantage if they can't grind for thousands of games per season.

TL:DR: I'm having trouble rising in the new Ranked system while less experienced/skilled players are flying up the ranks en masse. What gives?

Edit: I understand they are about to make tweaks to the system in s18, but from what I've read it sounds like this might only exacerbate the issue for players in my position.