I think the switch from Weaver to Isoceles has more to do with dynamic shooting issue than with body armour.
L/R upper body turn shooting is much easier/faster with Modern Isoceles than with Modern Weaver.
Also, most folks should learn to shoot:
- one handed, L/R (wounded, when one hand/arm is occupied)
- two handed shooting for recoil control
Also, know at least the basics of one stance.
FWIW, it doesn't always make sense to take cover/concealment and then shoot.
Depending on circumstance, sometime, it makes more sense to just shoot, even with increased exposure.
You need to balance the exposure time with how fast you can make the first accurate shot.