If your personal play is excelling at that type of level and you aren't consistently winning games its not your mechanical abilities holding you back.
You lack macro skill. Try to learn to make better strategic decisions, organize and coordinate your teams better, be a better leader so your teammates will want to follow your lead, be the guy coming up with a gameplan. You are so far ahead in your games that practically any plan you might come up with is likely to work. Give your teams a goal, something to focus on, "Lets ward up this half of the enemy jungle and 4 man that half of the map while top lane splits solo while he has TP. If they send 4 to stop our push and one to stop his we will back off and start the baron since we have vision control. If they send 2 after our solo we hard push and punish with 4v3 at this tower. If they send 5 to stop our 4 man we get free towers on the opposite side by stalling." This is the element of your game that is lacking. Learn to be a good communicator and team organizer, this is the most important skill to have in the game.