Sure- I was assuming otherwise healthy people in my comment. Yes, I could do it as a way around injuries, too, if need be. Most people I've worked with through mild chronic lower back pain have found the conventional rehabilitative, though some haven't, and I used sumo with one of them for a short time. I have also recommended it with CrossFitters when the WOD calls for deadlifts and they haven't developed the skill to consistently keep a flat back in hip flexion. Not a difficult skill at the light weights they use, but one that requires discipline and focus when you're doing 45 reps for time. There are a lot of things "not ideal" about that situation.
Also, for competitive powerlifters, if the back is the weakest link in the chain, a well-executed sumo will put more pounds on their total, and since that's what matters to them, all power to them, I suppose.
It sounds like we both agree about the situational contexts in which they might be productive... and for the general strength trainee, usually aren't.
Because magic, Hanley. Magic.
So far, I think Greg is trying to find a reason for sumo to not be heads and above superior to conventional for everybody, so he is working off of the idea that hip extension demands are the same, but they just aren't front to back, and as you point out, don't they just cancel out side to side? To me, I feel like he is not touching on the fact that force production just seems to work better with a narrow stance, i.e. we always jump narrow for max output. So less harsh moment in sumo, but less force output to meet it.
That said... yeah, not sure what there is to argue about Greg's stance on the quads here. Like... you can maaaayybbee get a brief start from them (and if you accept the Pulling Model of SS, you can't even start in a way to get any sort of real drive from them.) Other than that... they are basically at quarter-squat knee flexion with a hip-dominant strategy. This is not a difficult job for the quads.