Ralfy,
May I ask you the following question, since you are the author of that FAQ? (Well, there will be a question in the end, pardon the rhetorical questions along the way.)
When the razor is flat on a hone after a successful sharpening session, we agree that the entire edge (the very tip) rests on the surface of the hone, right?
After that, damages from shaving, stropping, etc. happen. You want to resharpen. You bring the razor and lay it flat on the hone. How far do you estimate is the edge removed from the surface on the average - a lot, a little?
The reason I am asking is the following. By my reckoning, convexed or concaved bevel does not matter as much as how far the edge has receded (= bevel has become thinner). If the edge has receded significantly, it may require quite a bit of honing before edge hits the surface. However, I never see visibly (not Veerhoven-precise, but estimated from 45X scopes) significantly thinner bevels before I need to resharpen. And, in few half strokes, the edge is usually on the hone's surface. Once on the surface, the abrasion it is subjected to is much fiercer than a mild stroke on glass. That is one thing.
Another claim about drawing over glass is that it will get rid of "bad" metal at the edge. My sense is that a proper hone directing highly abrasive material toward the edge, although at an angle, is quite capable of doing the same thing much better.
Bottom line: I can see that a highly receded (from diamond pasted strops, dished hones and the like) edge can possibly mislead a novice who might test the edge without paying attention to proper markers on the hone (such as undercutting slurry, etc). I suspect that would be a very small fraction of cases today. Historically though that would have been more common. Witness all the dished hones. And, we see all those scratch marks on the side of those hones too.
So, what do you think, do we really, really need this drawing on glass, or is it a ritual from the past? However inadequately I may have articulated this, Ralfy, I am more trying to understand the idea, and not at all trying to contest the possible usefulness of your FAQ.
I may be getting this all wrong. Or, sharpening too early. Let me know what you think.