Sure, there’s no free lunch, but there is the beat-you-up-and-take-your-lunch-money of not investing.
Bonds may have gone down, but they still paid out. Unless people sold at a loss for liquidity or could’ve timed the market and bought low, they were better off than people stashing money in a mattress or most bank accounts.
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.
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)
> 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.
Each of the asset classes you listed has risks. Bonds are subject to term (i.e. inflation) and credit (i.e. default) risk.
Bonds may be less volatile than equities and commodities, but they can definitely go down (e.g. 2022).
The only free lunch in investing is diversification.