Imagine the cryptocurrency industry without bitcoin. None of them will exist if Bitcoin is not around.
None of them would have existed without bitcoin, but (don't crucify me for this) if bitcoin suddenly went away, other cryptocurrencies could fulfill the currency role that bitcoin had quite easily. And while those forked coins aren't popular on this forum, it's hard to argue that right now it'd be much easier to buy something with pretty much any coin other than bitcoin.
Other cryptocurrencies can be used to transfer the value, no doubt in that! But bitcoin itself is
value. Tell me how many of the F500 companies would like to maintain a portion of their reserves in any coin other than bitcoin? None I guess. But they are happily adding bitcoin in their Balance Sheets.
Other blockchains may be getting their own space by providing smart contracts, cheap fees, faster transactions and all those stuffs but no matter how good they do, they will just be a medium to transact value, they can never become the value like bitcoin. And if bitcoin suddenly went away, believe me crypto market will die. If the strongest network can be taken down, why not the others?