Bitcoin has a lot of valuable characteristics, but its peculiar nature makes it more useful as a long-term investment, rather than a currency to use for small, quick transactions, with a cheap cost and a fast execution on the network.
Indeed, the electric and computational cost to validate bitcoin transactions has been increasing over the last years. Also the time needed to confirm a transaction increased, so it will take too time to purchase a coffee using bitcoin, for example.
image from bitsonline.com
This doesn't mean that Bitcoin is a useless technology, it just means that it's not currently effective as digital money for cheap transactions, or online micro-transactions (as imagined by Satoshi Nakamoto in his white paper). The extreme price volatility makes impossible to use bitcoin as a adequate unit of account.
It's not profitable to use bitcoin to buy stuff online, when its value keeps increasing. It is more profitable to keep the bitcoins safe into the wallet, and wait it to increase their value passively. Maybe it's wiser to use fiat money (with a 2% yearly inflation) to purchase goods, and use bitcoin as saving and investment.
image from archive.org
Bitcoin is rather digital gold, more a commodity than a currency.
Like gold, it is useful as a store of value; it retains its purchasing power into the future and is a rare, expensive good. Also, its value is not influenced by economics and fiat money policies. It's a transferrable, digital, non-duplicable good.
It may be dangerous as a short-term investment, because of its extreme volatility, but in the long term, it increases its value, just like precious metals do.
Hundreds cryptocurrencies today are competing in their ecosystem, to provide an improved model for digital money, as a cheaper, faster alternative to bitcoin.
image from Medium.com
Another possibility is considering the future option for bitcoin to have a more stable price, with low volatility. This may happen in the future, or may be happening right now, with the Bitcoin Cash and Bitcoin Gold forks. But we still need bitcoin as digital gold, to use it for investment/speculation.