Just speculating: Tinny does not appear to use any water in his baking method while Sarah does. That's probably the difference in baking time. If you've ever done much cooking (heck, even opened a bag of microwave popcorn) you'll know the tremendous heat that steam carries. You can stick your hand in a hot oven for a second or two with no damage. However, a blast of steam lasting less than a second can give you second-degree burns. Vicious stuff, steam.
Tinny's method essentially heats the pot and the rocks which, in turn, heat the air. He creates a low temperature oven using radiant heat from the chamber. It works but takes time. The steam method floods the area with heat very quickly, reducing the cooking time by putting the heat directly on the cooking vessel. Steaming, although cooking relatively quickly, does not produce a crust, nor does it brown. If you just want muffins or biscuits, either method would work. If you wanted a crusty or browned exterior, or maybe melted and slightly darkened cheese on a small pizza, Tinny's method is probably more likely to produce such.
I use a canister stove so I can't afford a 30-35 minute cook time. I am, though, dazzled that Tinny is getting 45 minute simmers from his stove. I have dabbled with alcohol stoves before, maybe it's time to take a second look.
Edit: watched the MBD baking kit video, he does not use water. One good thing about his method is that the rocks stay hot and continue to bake even after the heat is removed.