Ok, first of all, I have over 1000 hours in the game, allot of experience so I think I'm qualified to say the things I'm about to say.
One of the most common thing holding players back is when they blame there team mates for there mistakes, and they don't realize that they are doing it them selfs.
Yeah, sure you might be better than them, heck they could be wiffing 2/3 balls, but there is a reason you get matched up with him, you have the same mmr as him (Match Making Rating) "Yeah i have the same mmr as him because people like him are holding me back and therefor i cant escape that mmr range". But here is the thing you are defenently doing something just as wrong as him if you blame him for your loss.
Here, let me give you an example, he goes chasing the ball into offence to give you a pass or try to score, then you go in front of the enemy goal to prepare but then he fails extremely hard, does something really stupid, so the other team gets a counter attack and scores. "that was obviously his fault" NO!!! you failed, not him even though his attack may have failed, you completely misjudged the situation and left defence open and gave the enemy team a free goal.
Ok, now for another example you are in goal and the other team is about to take a shot so your team mate goes for a block but then completely fails and the ball goes rushing to your goal at 150 kmph and straight over you. "Yeah i was expecting him to make a challenge, so i went forward, but he failed, how was that my bad???". Again IT WAS YOUR BAD! maybe this time it was also your team mates fault but heres the thing there is ALWAYS something that you could have done better, no matter what. In that case, you knew that you had a 'bad" team mate so you should have stayed in goal, but you didn't, so again, you misjudged the situation.
Now those examples were very situational but you get the message, you can always prevent this stuff from happening. So please don't blame team mates for holding you back.