It's not inaccurately low at all. You're basing your estimate on perfect/ideal scenarios, I'm basing it on the kind of thing the average overweight person trying to lose weight does when they spend an hour in a gym. They walk on a treadmill or they do more intense things with a lot of breaks in between.

Also, there is no proper form of exercise for an obese person that won't cause pains or aches, it doesn't exist. We might just be coming from different backgrounds and talking about different body types here.