I agree, you need more heat. 250f will be like braising the wings in liquid. You'll get a softer, mushy skin.
My favorite way to do wings is first trim all excess fat with a poultry shears. You'll be surprised at how you can cut 20% of the fat from wings with some scissors. Wash and thoroughly dry the wings.
Then, preheat your oven to 500f, with a sheet pan inside. When blazing hot, put the dry wings on the sheet pan. They'll sear and brown very quickly.
Cook the wings on the top shelf of the oven to take advantage of the convective heat bouncing off the top of the oven. Turn and toss them frequently to brown on all sides. When they are crispy like potato chips, remove, drain excess fat, then toss with your favorite sauce.
This method gives a crunchy, crispy texture like being deep-fried without all the fat. And, if you trim most of the skin off, you're making a much healthier wing that tastes more like chicken than the fat that will coat your mouth.
High heat to caramelize sugars is my goal when oven-frying wings.