Yes, holding cash also has risks.

That's not really my point. I think one thing that gets lost in the "everything has different levels of risk" discussion is that many risk/reward profiles are bad. Calling everything a tradeoff is misleading. Banks are more than happy to capitalize on laziness and lack of knowledge (an American is more likely to change their spouse than their bank), so the balance between risk and reward gets thrown out of whack.

The simple term for this is Sharpe Ratio https://en.wikipedia.org/wiki/Sharpe_ratio

If you want to get really deep into investment theory, Beta implies basically everything is a good investment in small enough amounts https://en.wikipedia.org/wiki/Beta_(finance)

Though in practice, Beta is mostly irrelevant beyond a relatively simple portfolio https://finance.yahoo.com/news/warren-buffett-myth-more-why-...

> I think one thing that gets lost in the "everything has different levels of risk" discussion is that many risk/reward profiles are bad.

Yes, not everything is on the efficiency frontier for risk/reward. Eg cash is convenient to spend, so it can 'get away with' offering a worse risk/reward profile.

Yes, the Sharpe ratio is one of many ways to measure risk adjusted returns.

> If you want to get really deep into investment theory, Beta implies basically everything is a good investment in small enough amounts https://en.wikipedia.org/wiki/Beta_(finance)

Well, that assumes no fees, transaction costs and taxes, I think. And even without transaction costs etc, the theoretically optimal amount can be so low that it's not worth bothering with.