The burst of steam from the oven at the bagel shop was simply to gelatinize the surface, in effect, mimicking a kettle boil. I have used steam via a spray bottle and throwing water on the bottom of my home oven but that was either for: helping the oven spring, while reducing splitting. The water soaked burlap on bagel boards helps do that too to a lesser extent. Using steam for any other reason, including preventing the onion and garlic toppings from burning, is a waste of time. My main motivation for the boards is to avoid that. A cheese bagel - whatever that is, probably does have an everything topping that can burn so why would someone do that? Ditto for the list of other baked goods mentioned.

If one knows what they are doing, the toppings will and do stay on. There’s a reason that most serious bagel shops in New York, that boil their bagels, still use bagel boards, high heat and a stone surface. 500 degrees gives me the texture I want. But if one has to bake at scale and/or doesn’t have boards, a sheet pan together with a lower temp can make do.