> Demand for cheerios is elastic- people can substitute by buying oatmeal. Demand for salmon fillets is elastic- people can substitute by buying tuna, beef, beans, tofu, etc.... for just about any given food item there are substitutes to provide similar high quality nutrition.

This would be a good argument but I feel it’s undermined by the heavy consolidation in the food market, no? If the same company is selling each product, then it doesn’t matter as much if a consumer switches between them

I agree with the rest of what you said. I certainly don’t know how to prove which is more relevant but I believe the supply shock and excess money played the largest role, however I think it’s wrong to dismiss either as both seem to be at play.