Bitcoin can't be defeated I guess because the value of it right now is still biggers than anycoin in the cryptocurrency markets and even though the value of bitcoin today is not regular and not maintain it is not even close that bitcoin will be eliminated nor defeated by any type of crypto in the market. 2019 will be a good year for bitcoin I wish.
In the coming years, bitcoin may not be beaten. But if we already judge by what is happening now, then more and more people prefer Ethereum. Therefore, on the air, all shans win.
How can you say that now people prefer Ethereum? Considering the market cap, Bitcoin is higher on the rank meaning that is more powerful. Also, these two that you compare have different uses. The one is used mostly as storing value and the other for building Dapps that are helped due to the smart contracts.
In the end, they are not the same in order to say that you are going to use the one over the other.