My school of thought is that
something should be modeled - otherwise you're just writing code. The point of RPGs is that you get a story or a scene that you experience with other people, not rules for rules' sake.
. . . Sometimes the fighter can't get through the heavy carapace, so he's gotta try to hit the weak spots between the plating.
Sometimes the rogue can't get an opening; he's just gonna have to try punch through the armor. . .
My game does
a version of this, so I can tell you how
that system goes. Characters can try to avoid the dex/parry side, but the str/armor side is generally required defense...
Attackers can carry heavier weapons or specialize with their weapons to punch through armor (deal more damage). And/or they can increase their skill/ability/speed to hit "between the plating."
Defenders can use actions to parry which avoids all damage. All unparried or successful attacks have to go through armor, which reduces damage, but not down to zero.
Does this create a meaningful decision point? Indeed. Opponents with heavy armor must either A) get hit with bigger weapons or B) get hit a lot. Opponents who parry well must be surrounded/blocked or defeated quickly (before their friends arrive). It doesn't hurt for someone in the party to have a blunderbuss, which doesn't do all that much damage, but at least it can ignore armor (along with mental attacks . . . ).
A key difference from the OP suggestion is that opponents can't completely ignore one approach or the other - the GM can't say, "too bad you put all your points in strength. Now this opponent is going to require Dex only." Both attackers and defenders have decisions to make, and it always helps to have allies.