I think you misunderstand several things about how the system works.
Yeah, you get bonus MMR for winning streaks, but that is pretty rare. The more games you win in a row, the crappier teammates you have to carry each game. If you manage to win 5 straight, you are going to end up on a team full with feeders and trolls pretty much guaranteed since you will be paired with the lowest MMRs in your division. This is because as your MMR goes up, you become the top MMR player on your team. So the system pairs you with the lowest MMR guys to balance it out for the team you are going up against. It really doesn't matter how good you actually are when your team feeds like an all--you-can-eat buffet.
On the flip side, losing streaks are absolutely devastating. If you end up on one ( which is easy since you are now getting stuck with crap players), it literally takes MONTHS for your MMR to recover. MMR for divisions fluctuates continuously. This is why you end up with so many garbage players on your team so often. This is why they had to lower the requirements for each division, the ranking system has been so broken like this they had too.
The players that reach high ELO do it entirely from duo queue's 95% of the time. Several pro players have tried to climb out of Bronze intentionally and have said that it's incredibly difficult. That is why they duo, it lowers your chance of getting a horrible teammate by 20%, which is a HUGE advantage. Plus their duo q partner is just as good as them, so it makes it so much easier for them to get ahead and win games against the guys who are only able to solo q.
I know the next thing you are going to say is: "Just find a good duo partner". That isn't always possible since some of us actually have real world responsibilities such as work, school, etc. and it's hard to be able to find the right times to be able to duo with someone. Once again, this is something that makes ranking up even harder for the average player.
I guess I also need to point out that you looked at this account to see my MMR. This is my smurf account that I use to play with friends that are in Bronze. This was my main when I first started League. Once I started to learn how the ranking system worked, I realized that you shouldn't play ranked at all until you have really gotten the game down. Once again, this destroys most players since your MMR end up so bad while you are learning the game that you can pretty much never recover.
So the best advice I have seen is to not play ranked until you have a very solid grasp on the game. You can then go into ranked and rise up since you won't go through the phase of having a crap MMR that severely slows down your ability to rank up. So they don't need division below Bronze, they need to keep people from being able to play ranked until they have played X amount of normal games or have reached X amount of wins in Normal. That would do two things, keep horrid players out of ranked and have players who understand how to win in games in ranked