I recently converted to Modern Isosceles after shooting almost exclusively from Weaver since 1989. I find better recoil control with MI than with Weaver, when I use the techniques described in the Enos book and Plaxco's "Shooting From Within." Gun pops up, watch front sight lift, gun pops back down into same spot, fire again.
I actually find this faster and easier than fighting the recoil in Weaver, and I shoot a 1911-pattern .45. Controlling the gun in MI is more a function of the grip than the stance, so the body and foot positioning can be more relaxed. I see very few top-level competition shooters using Weaver anymore, even in the limited/stock divisions and IDPA, where compensated guns are disallowed.
I also note that former Weaver stalwart Gabe Suarez has changed over the years to what he calls a "fighting posture" that seems very loosely Weaver-based. He wrote a pretty good article about it in one of his newsletters a few months back.
All that said, I dispute the proposition that Weaver crumbles under stress. Graduates of Gunsite, Chuck Taylor, John Farnam, presumably Thunder Ranch, and others have shot very successfully from Weaver under defensive conditions. I do agree that Ayoob's severely stiff and rigid "Stressfire" Isosceles probably holds up better under stress when used by non-dedicated personnel, but I'm not sure we can make sweeping assumptions about stance based on the reactions of the ill-trained or non-practiced.
Logistar, the Weaver is an isometric stance that relies on forward-and-back muscular pressure to stabilize the pistol. However, if you use the stance correctly, you don't need to consciously push and pull. Just tuck your weak elbow as far under the gun as you can get it, so it points directly at the ground. This will automatically create the isometric tension that Weaver shooters use to control recoil. If your weak elbow sticks out like a chicken wing, you lose most of the benefits of the stance.
Mike
