An uninsulated thin gauge metal dome doesn't retain enough heat to do anything
Actually, Jeff, low mass, uninsulated ceilings can achieve quite a lot. If you're looking at this from an NP perspective, then no, thin gauge metal won't retain enough heat, but, for NY bake times, Kenji's work with the Kettlepizza insert points towards the viability of low mass domes for 4+ minute bakes.
Mass certainly helps, but, I believe that just merely stopping hot air from rising goes a long way in providing top heat to a pizza.
Now, Kenji did his low mass magic with foil and a (most likely) higher BTU wood heat source, so I'm in no way defending this oven, but, I think we have a long way to go in determining the viability of low mass domes.
Beng, what bake times are you seeing with this? Faster bakes exacerbate top/bottom heat balance issues. Things even out quite a bit with longer bakes.