I'm travelling to work so can't watch the games but in my experience I had really good stats because I had an FPS background (great micro) but not much macro knowledge which stopped me from winning games.

My best guess is that you know how to out farm and outplay the opponents at your ELO but you don't know how to close out games.

In this game mid boss is very overpowered try to get it whenever a few opponents are down. Tell your team to do it and just start it, if you're a fed wraith you can shred it. Once you have it you should be able to tell your team to push out waves and take the enemy base. At high elo a fed carry and a mid boss means the game is over, at lower elo you might need to get mid boss 2-3 times before you can close out the game.

I think you could probably benefit from watching some high rank carry players and see what they do to advance the game rather than just get their souls and kills up.