In an economic sense,
An INVESTMENT is the purchase of goods that are not consumed today but are used in the future to create wealth.
In finance
An INVESTMENT is a monetary asset purchased with the idea that the asset will provide income in the future or will later be sold at a higher price for a profit.
I really don't want to turn these into an economics class but the both definition of what investments are clearly should settle the argument of whether BTC is truly an investment or not.
Yes Bitcoin has become an investment whether we like or not but most people like Bitcoin as an investment because the profit they have gained from price increases and decreases but if it become a currency it should have a stable price range so investors will not gain much profit due to the lower variation but the down side of beinb a investin asset is Bitcoin will never become a global currency so there are both pros and cons