I think there are no one who mentioned that bitcoin can be beaten by altcoin because what we are talking here is speculative only meaning for altcoins and not concerning what would be for bitcoin.
That's clear and even if someone said it for Bitcoin, I don't think many people would believe it because it's been clearly proven that Bitcoin can't be beaten by any altcoin now.
So whatever will happen to Bitcoin for now, I will still believe in Bitcoin in terms of investing and trading in the market.