Place cabbage in a stockpot; pour over enough water to cover. Add 1/4 teaspoon salt; bring to a boil over medium-high heat. Turn cabbage every 2-3 minutes; transfer any leaves that separate from cabbage into a strainer to drain and cool. Continue to boil until all the leaves have cooked, about 15 minutes. Reserve 1 1/2 cups of cabbage cooking water. Cut out the tough, thick center ribs of any large cabbage leaves with a sharp knife.
Preheat the oven to 350 degrees F (175 degrees C).
Mix ground beef, ground pork, cooked rice, eggs, onion, fresh parsley, garlic powder, salt, and pepper in a large bowl until combined. Lay 1 cabbage leaf on a flat surface; place 1 heaping tablespoon of filling at the base of a cabbage leaf. Overlap with the bottom of the leaf; fold in side edges and roll up. Repeat with remaining large cabbage leaves and filling.
Cut any leftover cabbage leaves into pieces and place in the bottom of a roasting pan. Layer stuffed cabbage rolls on top.
Combine tomato sauce, reserved cabbage water, white vinegar, and white sugar in a bowl; pour mixture over cabbage rolls. Cover roasting pan with aluminum foil.
Bake in the preheated oven until filling is cooked through and sauce has thickened, about 2 1/2 hours. Baste stuffed cabbage rolls every hour.