This deck is definitely better off being straight Selesniya or Gruul. Makes your mana a ton smoother.
Another problem is that your deck is a mish-mash of ideas.
Shanna, Sisay's Legacy and
Shalai, Voice of Plenty don't beling in the same deck as
Fumigate and
Cleansing Nova (and I doubt they belong in this deck with how little ways you have to make Tokens).
Even in Singleton, it's important to formulate a cohesive gameplan, your deck seems to lack that. Are you a ramp deck that wants to get out fatties quickly while not dying? A tokens deck that wants to swarm the opponent? A control deck that wants to win off the back of planeswalkers and needs ways to protect them?
Sorry for not getting to this sooner.
You're probably right that this is a pile of stuff that doesn't work together. My idea was to take all of my best mythics and fill the low cmc part of the deck with mana ramp and fix. That's what I mostly face in Singleton - just with better bombs (mostly Grixis with Nicol Bolas). I kind of ended up in Naya, white for the Angels, green for the mana and red, I don't remember.
From my actual games, the sweepers have done more work and I wanted to draw them more often than the two creatures you've named. I think they are important for the ramp into bombs plan. I could have the issue of lacking said bombs though
But while I get that Shanna is only a glorified bear in this deck, I wonder if Shalai isn't universally good - even without a token approach?
For a 2-color midrange value approach, I could probably cut half the list. I'll post my Selesnya version later or tomorrow for you to inspect.
Thanks for your evaluation.