Putting the gun against a wall and all that mumbo jumbo of so many inches away is pretty much a useless way of measuring pitch.
Simply not true. Comparative numbers are comparative numbers. Pitch measured as inches at the muzzle or degrees of angle are both perfectly valid measurements and useful. Personally I've found the inch business far more utilitarian and of course massively simpler to obtain.
"For us mumbling simpletons, pitch can be specified as the difference between LOP to heel and LOP to toe"
Yes it certainly can but that is a meaningless number as any set of differences are meaningful only in conjunction with an also set number for the drop at the heel. Changing the drop changes the pitch even tho the heel/toe relationship remains the same.
