This is also all rather abstract when we actually use grades in context. Even if we simply have a picture with a line drawn on it and no description, when we are actually stood beneath a crag we take in a range of visual clues that help us make sense of a combination of letters and numbers on the page: does the rock look solid; does it look compact and hard to protect; how tall is the cliff; how steep; are the lines obvious or hard to read, etc. etc. Of course, having a guide book description adds even more information.
Ah, well that's all good as long as you are using grades for their primary purpose: to give information on difficulty to the aspirant ascentionist.
The problem comes when using grades to compare dissimilar routes in order to benchmark achievements, for example to compile a graded list where Century Crack is in some way comparable to Equilibrium. Leading to the reductio ad absurdum that WSS is harder than Right Wall because it takes most people a few more goes. Because E-grades consider the extra dimensions of risk and consequence inherent to trad, they can only be comparative within a genre – 'safe-but-sustained', 'bold-and-technical' to quote the Grit List from 25 years ago.
As for the H-grades idea, in my limited experience the E grades for harder climbs are indeed given for a hypothetical ascent without pre-inspection. That’s the only way a route such as Meshuga could merit E9: it’s straightforward if you have top-roped it, but working it all out going from the ground would be pretty exciting. At least comparable to onsighting Indian Face or Hubble