I absolutely agree with you, for the example is obvious at this very moment. According to the information of coinmarketcap.com, the market capitalization of ethereum is already very close to the bitcoin capitalization and possibly it would be exceeded in a few days. It is also presumed that ethereum is better and more advantageous than bitcoin, however that has not been an impediment for the bitcoin price to continue growing gradually along with the price of ethereum, and this same case could be applicable in future cryptos to come, as we have seen many other "new and revolutionary" altcoins arise out there and none of them has diminished the trust that people have in bitcoin.
People tend to put a lot focus on the market caps of certain altcoins, and that they might surpass Bitcoin at some point. But the reality is that Bitcoin by market cap is already surpassed. It just shows how insignificant market caps are -- market caps hold zero value. Even the flashy features that altcoins have as "advantage" over Bitcoin don't say anything. What matters is the level of actual usage that the coins experience. Till this day, nothing comes even close to Bitcoin in that aspect.