This is really something I think of as “fitness fluff”. It’s not really science, it’s a simple training plan that’ll probably work for >50% of the reasonably fit population. It’s also a training plan to accomplish a specific thing, do a handstand. It doesn’t really feel like a discussion on whether handstands are good and what regressions to apply where; why judge it so.
The bs and “real” science on nutrition and exercise both face a replicability crisis. The salt you take with all this bs (or studies, advice) will also help you achieve bigger pumps during hypertrophy training.
p.s. Don’t take the “bro” in bs too literally. It comes from all genders and identities equally. Anecdotally the biggest purveyor of bs in my life was a woman who went to med school. I still hear and say plenty of bs in my circle of crunchy climbers. You apply it moderately and trust your gut on what’s reasonable in the face of _massive_ complexity.