Seems like you lose so much flexibility/power by not having a Fallen Druid, I don't understand why you wouldn't include it? I can even see an argument for just having an un-upgraded Fallen Elf even without the Boneyard; I get so much mileage from him, just shrinking down dragons to levels that can be Oty'd, and making fireflies a little more useful/threatening. And it's such a huge chore to beat through certain shields/Feral Bonds with just Otys and the sole Queen, who can easily be in the bottom couple cards. With only 8 land your expected time quanta per turn is only 2; thus being forced to kill at a glacial pace can lead to getting time-screwed and subsequently decked, especially if you were forced to hourglass aggressively early for answers.
The Boneyard skeletons do multiple things for you also: a) Win condition with mutation is obvious, but not the only thing. b) They act as food for your Oty so he can grow big enough to take down >5 toughness creatures (i.e. Puffer Fish feeds into skeleton, feeds into 2/7 to kill an Abyssal Crawler). c) They can be butterfly targets (Who wants a stupid Pest in their deck anyway? I'd rather have a 3rd Oty, to increase the chance of seeing on in the first 5 turns). d) They suck out the opponent's point removal spells. e) When the AI/your Oty/mutation kills them, their death feeds your Bone Wall.
It's been said that bigger decks reduce consistency, and there's obviously some truth to that, but the bigger deck has an advantage I haven't seen mentioned: When you get to the endgame, you'll have more land in play. When your deck is constructed larger, you have to keep the mana ratio stable, so you'll be going to 9 or 10 towers. This means when you're at the end of the game, you'll be generating on average 2.5 time (and gravity!) quanta per turn instead of 2, and your chances of getting screwed on activating devourers or Eternity is much lessened.