Combine water, lamb chops, stout beer, large onion, celery, parsley sprigs, 5 sprigs thyme, garlic, 1 1/2 teaspoon salt, allspice, black pepper, and 3 bay leaves in a slow cooker to make broth.

Cook on High until flavors combine, about 4 hours. Let cool, at least 30 minutes. Place lamb chops in a resealable plastic bag. Strain broth into a bowl; discard solids. Refrigerate lamb chops and broth, 8 hours to overnight.

Combine flour, savory, 1 tablespoon garlic and herb seasoning, salt, and pepper in a brown paper bag. Add cubed lamb; shake until coated.

Heat 1 tablespoon olive oil in a large skillet over medium-high heat. Add 1/3 cubed lamb; cook until browned, 1 to 2 minutes per side. Repeat with remaining olive oil and cubed lamb. Transfer browned lamb to the slow cooker.

Skim fat off the chilled broth and pour into the slow cooker. Trim and bone lamb chops; dice lamb meat and add to the slow cooker. Stir in remaining 5 sprigs thyme and bay leaf, rutabagas, potatoes, cabbage, baby carrots, and small onions.

Cook on High until lamb is tender, about 4 hours. Discard thyme sprigs and bay leaves. Stir in leek, chopped parsley, and 1 teaspoon garlic and herb seasoning. Cook until flavors combine, 2 to 3 minutes more.