MMR/Placement Games (dropping 7 divisions)

In 2014, I ended up in platinum IV, not being too focused on climbing any higher with the amount of time I had to play the game and climb. As the 2015 season rolled in, I didn't do too terribly well on my placement games 6-10, and ended up dropping all the way to silver II. And here we are back at the end of 2015 where I climbed up to plat III. My question is, do I have to score 10/10 games to stay in platinum? Does Riot factor in where a player ends up in consecutive years? Will I have to climb out of silver every year dealing with players with half-baked knowledge and poor tactics? I am not being condescending but I struggle with the idea I have to piggy back a few players who aren't ready to move up. Plus, I waste time playing through 7 divisions..... I think it promotes players to rage.