If we say that BTS is speculation, then the same can be said about all other coins. Suppose bitcoin is defeated, what happens to the rest of the coins? They will also come under attack, and not because they depend on Bitcoin, but because the cryptocurrency will lose confidence in the whole.
Read carefully again.
There will be stable coins which will replace those speculative scam coins like Tether-printer, 2000 shitc...and the king BTC.
USDT, USDcoin DAI will be alternatives. And they are climbing up on CMC.