Nobody knows how the fate of Bitcoin in the future. Most likely, he will remain the first and most demanded among all, but this does not mean that there will not be many competitors around him who will fight with him for the first place.
No one altcoin can be better than Bitcoin. However, I think, the popularity of BTC also plays a great role - most of the people simply do not know anything about the other cryptos. They are ready to invest in the cryptocurrency #1.