Heavy-bomber efficiency versus battleship firepower

Would a Barnes Wallis-designed Lancaster with Rolls-Royce Griffon engines have been substantially better?

Not necessarily: heavy bombers benefited more from efficient multi-engine production, larger bombs, and high-altitude performance than from simply fitting the latest engines.

Heavy bombers did not always require the newest engines because several proven engines could move a large payload efficiently. The more important improvements were larger bombs and airframes designed to perform at altitudes beyond the most effective reach of defending fighters. The B-29 demonstrates the value of high-altitude performance rather than engine substitution alone. Against a battleship's sustained shell weight, however, even a large bomber delivers a comparatively limited mass of explosives in each sortie.