I think bitcoin is both an asset and a currency. What some people who see it merely as digital gold are failing to take into account is that once the Lightning Network is fully rolled out, microtransactions with bitcoin will once again be possible.
It is indeed a currency and an asset but bitcoin cannot play both role because currency means that it is being used as a mode of payment while bitcoin is just being use as an asset because it doesn't have the reliable network and the fast speed of transaction that the people are expecting for a cryptocurrency to be used as a currency.