To all fairness you are where you are because your average skill level is at that.
If you get to higher league it will not be a pleasant thing as you might imagine. Enemy team will punish you hard for your and your teammates mistakes. Inability to organize team objectives and counter-objectives or help other lanes carry themselves and game for you is your mistake. For example: instead of defending mid turret you could gank bot, get double + turret + drag.
In addition if you are behind in your lane higher leagues assume you at least do not die and feed. At higher elo this is many orders of magnitude more difficult. Reason is that if they detect you are the weak point, they assert pressure and 'come for kills'. If you start to flame or blame your own teammates or asking for help, requiring them to drop what they are doing you are puppet for enemies also known as 6'th member.
If you play assassin like zed, your job is as assassin to take out carry and possibly all others and live. If you are fed, you can split push as you can most likely 1 on 1 most of them under their turret with counter mechanics like zonja. This means they have to send 2 or more people to deal with you and remaining team is 4 vs 3 in your favor.
Idea is to push for your strengths. Know what you are worth and what you can NOT do. Going 20 0 and losing the game does not mean you played poorly - opposite, you did your effort. Accept that about 5-50% of times your matched so that you are not enough. Your job is not to win, but to play well.
Like Toua Tokuchi told to his team in One Outs : "Winning is about making your opponents lose, making them taste defeat, crushing a fallen opponent, kicking them when they're down, rubbing salt into a gaping wound. 'Winning is about trampling over corpses. 'It's not beautiful, it's BRUTAL." - Think about it.