I'd have thought that the vaguer grades of XS or HXS for sustained chop 4a or 4c would be more appropriate
I tend to think of XS/ HXS as being more suited to loose ledge shuffling, more like extreme versions of your 'E5 4a' approach suited to headstrong punters. And as I said above I'm very unsure of where the grade boundary lies.
Whereas our E4 4c pitch had more in common with Gogarth E5 5b like Death Trap - i.e. it's vertical, sustained proper climbing but you've very limited faith in either the holds or the protection. A proper trad E6 leader would have been fine, if perhaps slightly traumatised as I was. A headstrong E1 leader would either backed off or died.
or a VS up high after a 7a boulder (
(Edit: you've added more context) Clearly this would never have been given an E grade at all, because to anyone doing the start it would be trivial. As it is, it isn't trivial, and people back off it even with pads, so it got E4. E1 6a would suggest that the 6a is fall-offable but I would expect harder climbing at height than 'VS', but if it was dangerous 5b or 5c it would get more than E1 overall, so you can expect 5a ish I think. The grades are 'overall', they just cover a lot more variety than other systems.
I get what you're saying with this, but
I'm not proposing any changes I'm just explaining how it already works, and always has done. The proof is in the guidebooks.