I don’t think most of the Olam know or understand this issuer on the warming drawer.
I would also ask if the oven has a shabbos mode. If it does the answer might be different because in that case, it probably does NOT change the heat according to whether or not the door is opened.
On the other hand there might be a different chumra in regard to ovens and drawers which actually surround the food with heat rather than a belch which is open and only gives indirect heat from the bottom because the belch itself is hot.