Pemerton also believes that the feat has no underlying fiction, a controversial claim.
"I shoot him in the throat" = -5/+10. In GURPS this is "shooting for the eyeslits."
"I go berserk and smash his face in really hard" = Reckless + GWM.
If anything I'd say that it's Reckless Attack without GWM that has no underlying fiction.
The only really odd thing about 5E is that -5/+10 is that you need a feat or levels in Rogue in order to hit someone in the eyes, throat, or kidneys. Aesthetically I'd prefer it if -5/+10 were available to everybody, but that's not how 5E was built.
I can see your point, though I've never been a fan of Called Shot mechanics in any edition.
Final point: if you nerf GWM/SS, the next-most-optimal DPR combination is not necessarily going to be on a fighter chassis. It could be that Polearm Mounted Paladins become the next big thing in melee, and Necromancers become the next big thing at range. (The Necromancer can spend 5 SP per day at 6th level and a couple of hundred gold and have 4d6+20 ranged damage at +4 to hit on tap all day, which isn't really far behind the Sharpshooter Fighter with Archery doing 2d8+28 at +4 at the same level.)
That may be true, though I believe those options are far more situational and can be more easily managed by a DM.