Lethe
Captain
ancient bomber design of the1950s have a unique advantage: economic performance on long range high altitude subsonic cruise. Cheap to maintain, fly, and long service life. If you wanna use SDBs by direct aiming, you'd better get a stealthy flying wing; while if you wanna fire some big missile 1000km away, these old designs are the best choice.
H-6K and B-52 still have utility as ASCM carriers, but that does not mean they are ideal platforms for the task. If you were designing a dedicate ASCM carrier from scratch you would create a platform with modern engines (at least PS-90A standard) and modern aerodynamic design to maximise range/endurance. Even without VLO requirement, it's quite possible that a flying wing would be the optimal configuration for the task.