....and stand with it shouldered facing the target. Aim, and fire. Now, drop the carbine and draw your pistol. Do you really want to move your feet to get into what feels right?
If I read this right, you're saying that you can't realistically employ your carbine from this stance, right?
I very much disagree - assuming that you mean only the "true" iso stance. My above post indicated that I train people to fire both weapons from the same stance: shoulders square to the target, both feet pointed in the direction of movement and about a shoulder's width apart, weak foot forward.
You lean slightly forward at the waist, keep your elbows in, and bend your knees. If you're moving forward in this stance we've always called it either the "duck walk" or the "combat glide" - it provides the most stable shooting position throughout your movement because your lower body absorbs all of the 'bouncing' motion.
Transitions don't change your stance, either. Drop the carbine to the weak side, draw your pistol, and maintain. Shoulders are still square to the target and feet are still pointed forward.
I think the true Weaver stance gives you easy transition when you're not moving
. So I suppose it just depends on what you're practicing for.