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.
That is true Bitcoin has truly become an investment so purchase of Bitcoin from exchanges by buyers has been done with one target on mind and that is to sell for a highest price possible after a while imagining and assuming the price will eventually increase by time and the downside of it is no one spend even a little amount during that period for anything which makes even more Bitcoin to fail as a currency and this has been continuing since the beginning no matter with what vision Bitcoin was developed by developers