Very true. That’s why gains from pumping alone are very hard to attain. You have to couple it with a manual routine, like jelqing. I view pumping as an enhancer of what you are already doing. Just another piece of the PE puzzle, another tool in the arsenal.
The thing is if something only works when combined with manual exercises can you really say it works ?
To me that would put pumping on a par with warm ups, kegels or edging, a useful add on but no good on its own.
Nothing wrong with that I guess as long as you understand it.
You have to ask though if all the guys who gain with pumping as part of their routine would have gained just as well without it ?
I don’t think I’ve ever read someone say they weren’t gaining with manuals then they added pumping and started gaining.