I think bitcoin is not the first cryptocurrency, maybe because it is the first cryptocurrency that becomes successful since it is decentralized and no one can shut it down and they do not even know who makes it or started it. Bitcoin is the most used cryptocurrency as of now since it is the center of transaction because you cannot buy some other tokens if you don't have one. In investing also, most of the projects requires bitcoin when you want to contribute to them. Bitcoin has also awesome platform that makes every user comfortable to buy it and use it as a payments. There are lots of projects that are promising and becomes successful but they are being dominated by the price and volume of bitcoin. Thats why bitcoin is considered first, maybe in standing yes.