Whisk together the buttermilk, hot sauce, garlic powder, onion powder, smoked paprika, salt, and black pepper in a large bowl or gallon ziplock bag until fully combined.
Pat the chicken pieces completely dry with paper towels, then submerge all pieces in the buttermilk marinade. Cover and refrigerate for at least 4 hours or overnight (up to 24 hours) for best results.
In a large shallow dish, whisk together the flour, cornstarch, garlic powder, onion powder, smoked paprika, cayenne, oregano, thyme, salt, and black pepper until the spices are evenly distributed.
Remove each chicken piece from the marinade, letting excess drip off, then press firmly into the flour coating on all sides. Dip briefly back into the marinade, then dredge in flour a second time, pressing firmly. Place on a wire rack and rest for 10 to 15 minutes before frying.
Pour oil into a large Dutch oven to a depth of 3 inches and heat over medium-high heat until a clip-on thermometer reads 325°F to 350°F (165°C to 177°C).
Carefully lower 2 to 3 pieces of chicken into the hot oil using tongs and fry, turning once, until deep golden brown and an instant-read thermometer reads 165°F — about 12 to 14 minutes for thighs and drumsticks, 15 to 18 minutes for breasts, and 10 to 12 minutes for wings. Maintain oil temperature between 325°F and 350°F throughout.
Transfer fried chicken to a wire rack set over a baking sheet (not paper towels), sprinkle immediately with a pinch of salt, and rest for at least 5 minutes before serving. Keep finished batches warm in a 200°F oven while frying remaining pieces.