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.
It will not happen in the near future. However, the development of cryptocurrencies causes more and more pressure on bitcoins. For this, it can not be ruled out that in a while some of the currencies will replace bitcoin in the first place among cryptocurrencies.
with volumes that are so far away I think it takes a long time for other coins to replace bitcoin. Moreover, bitcoin reaches 70% of the volume of other coins. so it really needs a miracle for that