On a target at 25 yards, using an aggressive c-clamp gets me a significant advantage in split times. That advantage is much greater at 50 yards. I don't agree with the notion that recoil on 5.56 and technique to manage it is insignificant in terms of performance on target; recoil in terms of "whoa fuck that hurt my shoulder" obviously not being what we're talking about here. FWIW, at the conclusion of a 3 month course, an instructor came up to me and said that I was the only person in the class who ever shot him when reacting to contact in our force on force scenarios, and that I had done so multiple times.
I was also the only person practicing an aggressive c-clamp grip that actually gave a shit about shooting, regardless of the fact that we did a good amount of shooting and the entire class was taught the c-clamp. It's not just about recoil management...the other side of the coin is being able to drive that sight line to the target and effectuating good hits under stress. I think it makes an even bigger difference under stress when people tend to bounce around and stress kicks in....that's when you're very likely to push the muzzle around on your own by using a subpar technique as opposed to driving that bore onto meat.
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As for the larger question at hand in the OP, I think it's worthwhile to train well if you're going to train at all. Just like training point-shooting is dumb, training to shoot with a magwell grip is a non-starter. If it needs to happen it will happen, but there's no reason to not train in a more effective technique. What's the point of practicing to suck?
As for fatigue, I can't imagine that's going to be a factor in home defense scenarios.