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.
That is not the reason why bitcoin cannot be defeated, the high price of bitcoin is a sign of what it is behind it, the technology is the best and there are many users that do not trust in any other cryptocurrency other than bitcoin so bitcoin has the trust of almost everyone in the market and out of it and when you have something like that then it should be clear to anyone that it is almost impossible to beat it unless a coin appears and has a technology that is many time superior to bitcoin.
And we need to be realistic the chances of anything like that happening during the next years is low so bitcoin will keep being the leader of this market for a very long time.