Genuine question for RIOT about MMR, ranking, and placements

So S5 was my first season. I lost most of my placement matches and ended up bronze 1. Throughout the season I went up and down, going as low as bronze 4 and then eventually climbing my way up to silver during the pre season. I main support/adc but am getting better at other roles through practice and experience. I constantly work on my fundamentals in an effort to improve all roles. I play ranked 5's with friends who are gold, and duo often with a plat player. None of these people can understand how I am in this bronze bracket as I have no problems laning against gold players, high plats or diamonds are where I start feeling pressure. Getting to face strong opponents like that is why I loved the ranked 5's, it was a great opportunity to see how better players then myself pressed advantages or played out certain situations.

Here is my issue. During my placement series, I had literally 10 games of my teams mid and top lane feeding their opponents so hard the games were unwinnable, I managed to win ONE game by stealing 2 barons with leona. Loss streaks happen, I wasn't tilted or playing badly, I offered positivity the entire time and tried my best. Because of this, I went from silver 4 preseason, to bronze 4. Literally all of my hard work in improving my rank and getting out of that domain of pure toxicity in teammates was thrown into the dumpster.

So if I had lost 9 games from silver 4, I would probably end up bronze 1. So WHY have I dropped an equivilent to like 35 lost games? I would really appreciate someone from riot explaining this to me.

None of my friends from ranked 5's who are gold/plat players can understand why I am having such a hard time climbing out of this. Do I have to abandon support as my main completely because I cant carry enough to make up for players on my team feeding mid and top 10 kills before 15 mins? Because that is quite literally the situation I am seeing in 80% of my soloq games.

I am frustrated because I know I am improving a great deal in my own knowledge and gameplay, but that is not reflected in my ranking, I am going down instead of up. I try to always look to myself and what I could have done better in games, I record all my games now and make notes of mistakes which could have potentially cost me a win. But the reality is that in many many of the games I lose, it is lost because of several players on my team feeding over and over and over to create unkillable monsters of the enemy team.

I'm not here to whinge and about it, it's just a game, but I would seriously like some answers to the questions surrounding MMR and placements from Riot.