Thanks for the extended reply
Whatever else you end up doing, at least check that the random stats on armor won't eventually allow for a 100% reduction, that would at least break the game
The point about effort vs reward taken, but at least in A17 terms those Rad Bikers go from 3-shotting you on day one (40 damage per hit, 100 HP pool), to doing 4 damage (of 200 HP) at 90% armor, taking 50 hits for a kill - before any meds. From 3 to fifty.
Adding difficulty, ie adding sufficient damage to threaten at -90%, say "kills with 7 hits"
=> 200 HP / 7 hit = 29 damage per hit
29 is the 10%, so 29/0.1 = 290 base damage.. turns it into a oneshot until about 60% armor.
That 90% just isn't counterable.
I'd personally aim for about 75% absolute max in reduction, that's still pretty beefy compared to none, but would only quadruple the time-to-live.