Perhaps it is not right to disparage all alt-coins. Some alt-coins make you a lot of profit. As Bitcoin is the best cryptocurrency, comparing alt-coins with Bitcoin is not fair. Decentralization system is it's main basis.If you want to get more profit from bitcoin, you have to invest and hold for long term.
Believe it or not, the price growth of alt coins is completely dependent on Bitcoin. If you can analyze the market well, you can see that the price of Bitcoin fluctuates with the price of alt coins. But you are right that there are some alt coins which are promising to invest in and expect good results.
Not only long-term investment in bitcoins can be profitable, you can also earn more profits by investing in bitcoins short-term, but you need to buy a lot of bitcoins to invest in short-term. And if you use DCA to invest in Bitcoin, then you must hold it for the long term. Because using the DC method, investors buy small amounts of bitcoins either monthly or weekly.