This is a classic apples-to-oranges comparison. "Ethereum is a better fighter jet than BitShares because it has an olympic sized swimming pool." "BitShares is a better fighter jet than Ethereum because it doesn't carry around an olympic swimming pool."
Ethereum is good for prototyping. BitShares is good for scaling once the prototype is proven worth having. THEN you do the extra work to translate the smart contract into scalable form on BitShares.
But the bottom line is, all proven smart contracts will eventually move to BitShares if they want to scale.
BitShares will then upgrade to EOS technology, Ethereum probably won't.
RE: Why doesn't Bitshares dominate Ethereum?