But with that setup it's not a simple attack it's a sniper rifle and your face shouldn't survive without edge. he wouldn't in any previous edition either. It would make up the damage point loss on apds ammo but not as often as you think. Maybe +2 little low probably another 4pt difference would be manageable.
Or it's NPCs using Assault Rifles from a safe distance. And that's assuming we don't get even more AR buffs available in the future.
I do want smaller benefits, already am designing a houserule for it, but the big damage buff is just too much for me. Apparently you want combat to be incredibly lethal, and enjoy forcing your players into an arms-race. I don't. So I believe your motives are more a 'hey I want things far more lethal, so I consider the system broken' and less of a 'hey I want to add more granularity to AR-DR'. Which is fine, but then your rule doesn't have to make sense to us, just do your thing at your table. You don't want a balanced houserule, you want players to fear dropping from a single shot.
Anyway, I think you're heavily underestimating how easy it is to break your rule with high ARs and high DRs (as you showed when you believed 20 AR is only plausible for a Troll with a Combat Axe). So far all I did was focus on 'easy to get high ARs for grunts', but how does buffing the Troll to 9[13] Body, 8 Armor, Cover IV, +10 DR from buffs, +4 DR from augmentations sound? That's DR 39, aka 'oh that AR 17 attack needs to do 14 damage before there's a decent chance some gets through my soak pool'. And if you encourage super-lethal combat, you're basically begging your players to do that to survive your encounters. That's not an arms-race I consider any kind of fun myself, so I disagree with any houserule that encourages such.