10 years ago Bitcoin was not so popular but instead of time the demand for Bitcoin has increased a lot and the price has also increased a lot. Now if you look at the performance of 10 years, Bitcoin has done better than altcoins, Bitcoin has been the best in the past and will be the best in the future. Yes, you can expect to make more profit than Bitcoin by investing in Altcoin but Altcoin is very risky, you risk losing all your money here, and you don't know which altcoin will do well. You look at popular currencies like ETH and SOL, how well have these coins done in the last 5 years? On the other hand, if you invest in Bitcoin and hold on for a long time, you can expect profit, although the price of Bitcoin will not increase quickly, but hopefully at some point in the future the price of Bitcoin will be 1 million dollars, which is a matter of time and I agree here that it will not be like in the past and should not expect to make a profit like in the past.
Altcoins have always been my second choice no matter what. Bitcoins have been my preference and will be always. This is the mentality most of us will have even though we have a major chunk of portfolio filled with altcoins. Altcoins too can be a better source of investment if compared to other assets, but bitcoins will always be the mother of cryptocurrencies and will remain on the top. Majority of people who have investments in cryptocurrencies have bitcoins somewhere on their portfolio.
Few prefer holding bitcoins for longer duration while few prefer trading futures to make good money for short term. Bitcoins have given us the opportunity to invest freely and let's not forget, altcoins exist only because of bitcoins. Even I can see bitcoins going above and beyond in the future and that is the reason I would always keep a chunk of my portfolio with bitcoins. Even if bitcoins show steady growth, I can still be assured that the profits will not wipe out, and the investment will carry minimum risk.