Bitcoin is the only coin to hold for a long time to earn from cryptocurrency.
It's not the only one, but it's probably the best one among all that can be held for long term.
A person can earn good amount from Bitcoin if he invests for a long time.
True but depends on the level of growth from when one buys and till when they sell their assets back. Buying during the peak and panic selling during the bear market wouldn't give the same output though it can be long-term logically.
There were many tokens in the past that are now dead, and investors who invested in those tokens lost a lot of money. Most shitcoins pump for a short period of time, but later those coins turn into scams, once those coins die they have no value.
Financial markets such as the cryptocurrency market require an investor to do thorough research and analysis before making any investment. If you go all guns blazing in trying to create great wealth through newly launched coins and tokens, you will probably face the consequences.
If we invest for the purpose of making a profit, we can never invest in any other coin except Bitcoin.
That's not true. There are several other cryptocurrencies that can also be pretty profitable apart from Bitcoin, though the trust level differs between Bitcoin and them, they are not all completely useless.