The limited supply and the distribution process leads to the analogy of gold. It's not hard to also see the similarity of something that was once a universally used as currency also being considered an asset and therefore an investment. While I don't disagree with what you say I think it is inevitable and unavoidable that many people will view Bitcoin as digital gold and an investment.
we all know that it is like an investment and there are more investment use by bitcoin so I agree to you that it is an investment because of the similarity in gold. Yes, it is currency but the price was like a stock market that the price getting bigger and larger but sometimes the price fall into a cheap price.
It is a part of an investment because you can gain profit.