As far as I know, seasoning on a cast iron is polymerized fats only, from an intentional application. Other food residues (are supposed to π) wash away. Having actual food residue seems like a health hazard, as well as affecting the flavor of your next dish.
Discussion
I'd take some discoloration vs. Any nonstick poison coating on a conventional modern baking sheet. You could also use parchment paper or silicone baking sheets (if you trust the silicone) to prevent stains on the pans.
I tend to not care too much about stains on the enamel. But if you do, the only way to solve this issue is to spend a lot of money. π
I avoid nonstick coating like the plague, donβt worry!