Haha ok! I've had that feeling a bunch of times, where you figure out you shouldn't have been doing something and you're just like "wow, I'm like the worst human being ever". I totally get it on wanting to be the best mom ever, we all feel that way. And I think we've all had friends who are like "why the hell are you doing _______ with your dog?!".

My pup Link is 9 weeks old, and I "run" with him on a long stretch of soft squishy grass that is about 2 blocks long. He loves it and it does the trick of draining his energy, and I feel that this is perfectly safe for him and his joints. It's on leash, but I let him set the pace (quite a good one in fact) and run along side him. I suspect the surface hardness is more critical than the structured aspect or the time.

The length of this stretch and the vigor he does it in is nothing compared to what I saw him and his brother doing together last week!

This along with some mental stimulation from a pick-the-cup-with-the-treat-in-it game and he is out like a light

It actually is partially the structure that is the problem. When the puppies are running around on their own they will stop when they need a break. When you take him running in a more structured environment, even like what you are doing, he will be compelled to keep up with you even if he's tired or needs a break.