How much have you used a real post digger to plant real posts, not landscape timbers in soft ground? It will give you a workout and yes you will feel it in your legs. As far as weight lifting no but it is a great work out. There is always hauling feed and bucking hay to work on the weight lifting aspect.
Granted it’s a great workout, no disputing that. But you called it a great piece of “body-building” equipment. Body building is generally associated with adding substantial muscle mass and post hole digging isn’t going to do that. Now lifting and throwing hay bales is another thing altogether. Lots of those humongus college football linemen got that way from hay bales and hauling feed - no doubt. I think we are in basic agreement though - someone who works a hard farm life doesn’t need to worry about going to the gym.