Bitcoin will remain and will always be called an investment as long as there is demand. Bitcoin is compared like gold and that alone is enough reason for bitcoin to be called an investment. Bitcoin maybe created as an alternative to fiat currency but bitcoin found success as an investment instead of a currency.
There is a demand for potatoes too but you don't see people speculating on potatoes, going to the supermarket and buy some to hodl in the kitchen. If Bitcoin found its success as an investment as you say, so Bitcoin will never be accepted by governments and institutions to be used as a currency and so Bitcoin will never be a mainstream payment method. It(s also why we have regulations related to investments instead to get regulations as a currency