If I understand you correctly, you're saying that p-values are useful when used once to evaluate preselected hypotheses with preselected thresholds. This is a common defense of p-values.

Here's what doesn't add up for me: this implies that for many configurations, p-values are invalid. But what was it about preselecting the experimental conditions that really makes them any different? What makes initially chosen hypotheses of higher quality than iteratively discovered, "p-hacked" hypotheses?

The need for careful selection of a limited set of variable combinations in advance seems symptomatic that the test being employed is not robust. I'm not convinced that even limited application of p-value significance testing is actually valid.