First of all, I am not a LEO or a certified trainer so the following are questions and opinions that I have developed in my 10+ years of shooting. I do not claim that any of the techniques I use are better than anyone elses. So with that said...
What any weakness in the Modified Weaver assuming you aren't wearing body armor? I'm not too sure about the strong hand over powering the weak hand part. Does this mean the shooting hand is pushing more than the support hand is pulling?
One other thing is I believe that muscle memory is going to play a major factor in a high stress situation. Basically, what you practice most will be what you revert to when the poop hits the fan. I even at the range, I practice a modified Weaver stance. I feel this is probably what I would revert to instinctively if I was in a bad situation. (There is always a possibility that I will be cowering in some corner soiling myself too but I hope that won't be the case!
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While the isocoles presents a target that is protected by body armor (assuming you are wearing any), you are still presenting a LARGER target. I have never been shot (thank God) but I have heard that even with body armor, it can be pretty painful. If the officer gets knocked to the ground, they will still present a large target for the bad guy to shoot at. I prefer the modified weaver as I present a smaller target and stand a lesser chance of getting hit at all. At the same time, my support arm is covering my chest and will reduce the energy of any round that strikes there. It may still be a fatal injury but I don't wear body armor anyways.
I also like the modified Weaver since it is a forward leaning stance. This helps to control recoil, as mentioned, and also sets you up to fall forward if you were to be hit. I assume this makes it easier for you to continue fighting. At least that is what the mall ninjas and internet warriors claim. Heck, it makes sense to me.