One thing I thought might be possible is adjusting very strong monsters attacks by the amount of armor worn... so the less armor you wear the less likely his strength is being thrown against your shield/armor.
So a leather armor using character in fact has only 2 AC "going against" the Giants Str.... a full plate armor is 8 AC "going against" a Giants sheer strength. Thou I do agree that part of the strenght goes into better weapon handling and speed... not all or most of it does.
So if for example a giant has +6 Str to attack... he would get that fully vs. Full Plate Armor. (In other words no change) and against a nimble leather armor he would get only +2 Str bonus to hit corresponding to the 2 AC. (So a -4 to attacks in this case.) A Breast Plate at 5 AC would mean the Giant attacking with -1 penalty unless a shield is carried too.
Formula = Str Bonus - Armor of the "target" = penalty to attack.
This would make fighting Giants better with little armor... or a lot of armor in fact... not sure that is a good thing...

You can create a different scale... half the AC difference being taken from the Giants attack. So leather would provide only a -2 to the attack... no armor would mean a -3. I think this is best:
2nd better Formula = (Str Bonus - Armor Target) / 2 = penalty to attack.
+6 str - 2 leather = 4/2 = 2 penalty attack
(Bigger giant) +8 str - 2 leather = 6/2 = 3 penalty attack
No Armor +6 - zero = 6/2 = -3 attack penalty
+8 - zero = 8/2 = -4 penalty
Heavy Armor +8 str - 7 Breast and Shield = 1/2 = 0.5 = ZERO
+10 str - 7 breast and shield = 3 = 1 penalty.
Really heavy armor shouldnt penalize thou... (+10 - 12 magic armor = +2 to hit.) Only "negative" results. Your trying to survive those hits with sheer metal vs weapon.
Most higher level PCs have magical armor... so the AC bonus usually isn't too far from the Str bonus... and some creatures even thou they are very strong seem nimble enough in that their attacks aren't Strength mostly based. DM adjucates. Monks will benefit way more thou from this... which in a low magic/low power world to a medium power world isn't that bad actually.
Naturally once that big weapon connects... the full strength hits and damages accordingly.
Just a suggestion... feel free to ignore
