Very little time today, and probably most of this week. So not read all the above properly, hope I've not misunderstood the gist. But very quickly:
"I've always had uk 7a starting around 7B up to 7C+ ish, with 7b covering 8A and up"
But that isn't how it's actually used right, except for on a small subset of micro grit routes?
Indian face gets 6c. (ie: a Fr7b+)
Rhapsody gets 7a. (ie: a Fr8c+)
(And given time, I could give more examples all day).
That isn't a frickin useful technical grade.
Whilst he didn't like it when I said it earlier, the truth is that as far as I can tell, JB tends to think about this stuff in terms of a particular subset of short grit bouldery routes. Sure he's climbed longer safe stuff occasionally, but it doesn't seem to affect his views on grades as that's predominantly not what he's thinking about.
And perhaps more importantly, he has zero interest in headpointing (and indeed a lot of disdain for it), and so has no interest in a grading system that hangs together upwards of E8 (which is primarily where all the bunfights around this stuff happen and where we need a better system going forwards).
"if I recall correctly, is something akin to Xeno's paradox where any move can be subdivided into components no harder than 6c"
No, it has nothing to do with that.
It is the fact that for hard trad routes, all the people climbing them (even hard trad specialists) have climbed way way more things of that physical difficulty as sport or boulders.
And so they compare physical difficulty via the hundreds of similar level sport or boulders they've climbed, vs the one E10 that might have had similar physical difficulty. That's just how it is. You can complain about it all day, it just isn't going to change the reality of how people talk about physical difficulty on hard trad routes.
(Obviously there's all the separate issues around the tech grade not having a clear definition, being supposed to be the grade of the hardest move, but never really being used like that etc - put the crux of right wall or positron on the ground and they would be 4b). It works fine up to around 6b, above that, it just isn't useful, has never been clearly defined, and everyone climbing hard routes stopped talking about physical difficulty that way a very long time ago.
Could say a lot more.
I may not get time, but If I get around to it in the next few weeks at some point, I may try and put together a very quick attempt at a graded list of everything out there over E9. At which point when everything on the entire list gets 6c or 7a, with maybe one or 2 7bs, the argument about the pointlessness of the tech grade makes itself.