This year's ranking system, fair or unfair?

Hello everyone, obviously I'm sure you've all been bombarded with threads dictating, "I was Gold last season now I'm Bronze", or "Rito why does your system suck so hard". Well, I'd like to add to this list... just kidding... mostly. My placements this year went better than I expected, I won the first 2, lost the third, then won the next 5, and lost the ninth, and then won the last one. However, I am a little troubled about how players are matched and placed this season. For instance, in many of my games I played with an against Diamond (during my last 5 about 3/5 players were diamond on both teams), and with Platinum players. I figured that this was a good sign; my MMR was higher than my last year ranking now (Ended Plat 2 98 LP last season), so I must be headed towards Platinum 1 or lower Diamond.

So when I completed my series, I was somewhat shocked to be placed in Platinum 4. Now remember, I am not here to complain about the rank I received, but to shed light on a perhaps injustice in the system. I am not completely certain how I can play with and against last season diamond players, players who some of the time had better skills and mechanics than I, and be placed in Platinum 4. This goes for many other players as well, if they play with and against previous season higher ranking individuals, is it fair to place them well below those players whom they defeated?

Sorry for the long post, but if you took the time to read it, then please comment below if you believe it is just or not. I'm not looking to start an argument, just see if I'm getting my facts correct.

Thanks!