It’s an opinion. Obviously he’s not an idiot but he’s basing his opinion on his experience, research on pumps and extenders and reading forums.
My experience is different from his. For example hanging, pumping and extending (run as separate routines) gave me zero gains but potentially I’d got maximal gains from manual exercises and potentially I didn’t hit the sweet spot with devices that I managed to hit with manual exercises.
The main problem with PE is explaining to people the amount of force required to make a change. People only have their own experience to fall back on when explaining this and it’s very hard to explain (especially with manual exercises). But, all the time, you see people who have gained slowly or not at all change their routine and suddenly start gaining at speed. It would be great to have research into this but remote, self reported research has limitations and in-person interventional research over a 6 month period would be extremely expensive.