Good question!
I think the Spiti was developed in very dramatic way without Mitchell. The Spiti I wing span was 36 ft 10 in, lenght was 29 ft 11 in, max weight 5819 pounds, max speed 362 mph. The Spiti 21 span was 40 ft 4 in, lenght was 32,8 ft 8 in, max weight 9124 pounds, max speed 457 mph.
Maybe Mitchel would live longer, he wouldn't develop his beautifully little fighter such a aggressive way.