All cryptocurrency is Bitcoin and Bitcoin is all cryptocurrency. It is the default cryptocurrency of choice at this moment, and it is the reason why most people are investing in altcoins: to earn more bitcoin. This will remain so for quite a long time as the mainstream will need to adopt Bitcoin first.

However in the long run I do not see Bitcoin remaining the most important coin. Perhaps it will be the most valuable in market cap, sure, but I think we are going into a world with many cryptocurrencies living side by side. Which is the original Bitcoin or not matters little really, they're all useful and valuable in their own way. Right now you have people preferring Ethereum as their default currency. Focus will continue to keep shifting.

On one hand people have trouble wrapping their minds around the revolutionairy aspects of Bitcoin and it's decentralized nature, but I think people also need to readjust the way they view currency as a whole. Cryptocurrency will, I believe, forever remain fluid and changing. There is no stability or absolutes you can rely on; that's the old world. Crypto's will come and go, be replaced by newer versions and so on. Value will be determined by whatever people perceive as valuable - and nothing is forever in the world of IT. Blockchain may be internet 3.0 but one day we will have internet 4.0.