As far as I could determine, it's something on the lines of 3000 STR doubles reduction due to wdef (to 1 damage per def point - or about 400-500 extra reduced on decent level monsters). More typically you can expect 600-1100 STR on a 4th job character, which is only bringing it up from 0.50 to 0.55-0.65 per point, for maybe 80-100 extra reduction (compared to having no STR at all).
However, they did some kind of equalization based on the "normal" class STR, so the other classes get more damage reduction without STR. A str-less warrior takes far more damage than any other class (literally 200+ damage from Snails at high levels)
And you're right, against 6 Fire Targets, ACB totals 3780% while Brandish is only doing around 3000% to 3 of the targets. Against 5 targets it's almost even (3150%), against 1~4 Brandish is stronger and obviously does not stun.
However, they did some kind of equalization based on the "normal" class STR, so the other classes get more damage reduction without STR. A str-less warrior takes far more damage than any other class (literally 200+ damage from Snails at high levels)
And you're right, against 6 Fire Targets, ACB totals 3780% while Brandish is only doing around 3000% to 3 of the targets. Against 5 targets it's almost even (3150%), against 1~4 Brandish is stronger and obviously does not stun.