That’s a fair point. Effectively what your saying is that a linear measurement is useless because all the important stuff is happening in the top 10% or less.
I can’t believe that when people talk about jelqing at 30% erect they actually mean something near to flaccid.
OK then, we need a logarithmic scale.
That decided, actually creating one that makes sense to people and can be easily gauged and measured is a much harder task.
I suppose pressure might be a method of achieving that.
For example how much roughly can you compress the width of your penis (or girth maybe) at full erection, at 90%, at 80%?
Maybe not.