If you look at the Yessis blog post and at some of the comments on it it is very revealing.
What it shows to me is that even "authority figures" like Yessis (look at his background) can do lazy overgeneralizations couched in pseudo-scientific terms.
In this case the overgenerization is "dynamic versus isometric". It is REALLY stupid if you know anything about mobility, stability, and the function of the core. But if you've only read some roundabout stuff on the effects of dymamic movements versus isometric holds on performance you could easily get confused. But it's a beginner's mistake being preached by a Phd! Just goes to show how easily it is to be mislead in this industry.
Comparing situps and crunches to planks (and related) is not about comparing dynamic to isometric. Because we are talking about fundamentally different functions.
You compare an isometric press (or static hold, similary) to a bench press, lol. You don't compar core stabilization movements to abdominal flexion (hip flexor flexion as well)...even if you believe that situps have their place in terms of performance, which is debatable.