After play testing your deck I feel that you need to try to do less with it there are so many variables I stopped at turn nine because at least with my group if you haven't won by turn five or six then you've lost unless playing edh try cutting cards and adding play sets i think that that will help greatly. I do really like the idea however it is a start.

Maybe add Ojutai's Command?

I agree with zachblak. Consistency is key in midrange, and this deck doesn't seem like it really has a game plan. If you figure out what you want the deck to do, you can pick a smaller number of creatures that help you achieve that goal and run 3-4 of each, which will greatly improve consistency.

Without 1CC mana dorks 20 lands is too little. Especially as high of a mana curve you have. I can't imagine this deck gets going quickly. Bant usually runs 4-6 mana dorks and focuses on the 3CC drops 2nd turn. This is where it's power lies with creatures. But other competitive strategies are viable, as well. Speaking from more tournament worthy decks I've looked at.

Wont Sword of Feast and Famine make it so you cannot target your creatures with your green buffs?

You could probably cut down on Imposing Sovereign, because against some decks it does virtually nothing. Put one or two in the sieboard and put some other cards like Qasali Pridemage or Meddling Mage in that spot.