There is absolutely no need for Bitcoin to destroy the altcoins. Altcoins are altcoins and Bitcoin is Bitcoin. Lets not compare apples to bananas here.
Bitcoin has been the king of "crypto" ever since day one and that has not changed, throughout all these years. You should view Bitcoin as something which is separate from Altcoins. Each of them is different in their nature. It would be better to not even compare the two.
But also, lets not call all crypto a scam. DeFi is quite useful, as long as you know what you are doing and avoid the known traps.
Bitcoin and alts can co-exist with each other. They are catering different purposes just like we need ETH network for smart contracts.
There are several valuable alts that we need other than bitcoin. Just make sure you are choosing a valuable one and not just a pump and dump coin.
Thousands of alts have been created, but we are seeing that only few of them are in the top serving the crypto community.
And there's no need for bitcoin to destroy those crap alts, they die on their own if they don't have actual use case in the market.