Bitcoin is only 40% of the total market cap. You should not buy ONLY bitcoin as it is only one currency with its own niche.
Rather you should create a diversified portfolio based on the 10-20 biggest cryptos.
Each cryptocurrency has it's own niche and goals. For example, Dash and Monero are used for anonymity. While ethereum is used for smart contracts. Ripple will be used by banks to transfer funds internationally.
There are over 500 Cryptocurrencies out there to learn about.
So no. Buying only bitcoin is bad.