Your picture makes me nervous when I see it. Mmm.
I checked last night at full temperature and mine has a same similar non-flat surface. I was hoping things would be different when the stove was cool this morning. Unfortunately, I/we have never noticed this condition until now., The humped surface seems to follow the flame/heat pattern, and slightly discolored paint.
View attachment 255999
It would be nice to know if an unburnt unit is flat.
The thickness of the top plate was one reason we purchased it. I seem to remember one other brand with thinner steel, the user posted a photo of a [Edit-concave] top surface.
[My surface appears symmetrical to the flame patter. 1/8" out at the vent connector and 3/16" in the center toward the throat].
Good find. This is something I will monitor.