stocks give you ownership in productive companies. those companies on average go up in value and produce profits which they throw off as dividends (or re-invest to increase their market-cap).
so one difference then is that stocks have a justification for their returns given the variance you experience.
I would tend to subscribe to a similar view and think that no, gold is not really an investment. A hedge, a gamble perhaps. An investment is something that (hopefully) enables useful work and productive endeavour.
Putting money into a company in return for a share of ownership is an investment. A lot of stock market shenanigans are little more than gambling. Gold and crypto-currencies for the most part are speculation.
Although it's not always clear with ICOs if any form of ownership is conferred or what the relationship might be between future profits and token gains.
But yes, in principle.
--edit-- to be clear, I'm not trying to say one class of thing is better than the others, just that to me the words have different meanings.
so one difference then is that stocks have a justification for their returns given the variance you experience.