I have a steel version of a large griddle intended for use over gas. I bought it when I built a large chuckwagon box for hunting camp. I used it a bit (How many hunting trips can you go on with a 125-pound box?).
Anyway, it’s well thought out, what with turned up edges, a drain trough and handle. It’s about 3/16" thick. But the most interesting aspect of it is that it has a diffuser plate welded to its underside, intended to moderate the inevitable center hotspot. It makes it more even than it would have been, but it’s still no great shakes.
When I was involved in hyperconductive cookware development, we prototyped a double griddle to demonstrate what evenness was attainable over a wide area. They were about 13" x 21" x 1/8", and the coldest points were within 5F of the hottest point, no matter where you heated it. I still have one somewhere.
