I stopped buying the best named brands and switched most of my cereal buying to malt o meal brands, didn't really notice a difference.
But if malt o meal went from a 60oz bag to a 55oz one you’d probably still continue buying it rather than switching to something else.
It’s OK to be elastic for some purchases and in-elastic for others. Very rarely is price per unit the sole criteria for a consumers choice.
My grocery budget is $100/week, which I break into two $50 shopping trips. I will swap to cheaper brands than I am accustomed to in order to or remove unnecessary items all together in order to fit my budget.