Bitcoin currently suffers from a serious scalability issue with no solution on the horizon. Ethereum constantly gains greater acceptance and hosts an increasing number of projects on its blockchain. When will the inevitable occur? My opinion is that in about one year the marketcap of Ethereum will be greater than that of Bitcoin.
Most people who talk about the market cap of Ethereum surpassing that of bitcoin either don't understand the technology behind bitcoin and ether or they limit their valuation based on price.
Just because Bitcoin and ether are cryptocurrency does not mean that they are the same. Ether is focused more on dapps and smart contract than bitcoin
So rather than think of comparing them, I would focus on looking at the possibility of them solving their issues