Let me rephrase: The problem is that Bitcoins will have an advantage over the average productive investment, e.g. stocks (sort of), as a store of value, since Bitcoin has all their average expected growth with none of their added volatility.

I like the rephrasing. To expand on what seems to be a generalisation of this problem: Any cryptocurrency sibling of bitcoin that relies on cryptographic mining as a basis will either have this problem or will result in (value of currency * inflation rate) additional resources wasted on computation each year.

I believe (tentatively) that the above is an unavoidable result of the cryptographic and micro-economic principles that such currencies rely on.