The world is a big place. If you haven't seen stalled performance horses with stereotypies, then you know not of what you speak.
Yes, I'm sure I could find stalled horses with problems. I'm sure I could find pastured horses with problems. It isn't the corral or pasture causing the problem, but neglect and not caring.
My horses have good feet - but their corral is dry, very firm, even rocky in places. If I let the poop build up 12" deep or put my corral in a marsh (not likely around here), then their feet would suck. And I've seen 'pastures' that were more swamp than pasture...
I've seen too long hooves in horses in corrals and pastures. Neither setting makes the hooves bad, but a lack of trimming.
Maybe I am lucky. Around where I live, within a few miles, all of the horses I've seen live in corrals. They also have good feet, are not fat, have muscles and are showing no easily visible signs of problems. None of the people I associate with are having any health problems caused by corrals. One has allergies, and one apparently was purchased with a so-so leg. That is it. I've had 5 horses living on my property for at least 6 months. One was a 2 year old that was basically given to us, and I gave her to a trainer who now uses her for lessons. Another was sold to a couple who live about 1.5 miles from here. She is still living in a corral. According to the farrier we share, Lilly is doing great. And the vet and the farrier say my horses are all healthy...so it seems this completely inexperienced owner has been 5 for 5 in keeping healthy horses in a corral.
Since none of the horses I know living in corrals have problems, I conclude that living in a corral does not cause
problems. From what I've seen, stupid and neglectful owners cause problems, and will do so regardless of pasture, corral or stall.