Why a longer-serving Zenker would not transform the German Navy

What would the German Navy look like if Admiral Zenker survived in good health and remained in charge until at least 1939?

Not radically different, because Raeder shared much of his planning and both were constrained by industrial capacity, budgets, and political preferences.

A longer tenure for Admiral Zenker would leave broadly similar naval plans because he and Raeder already worked together on them. Zenker might win particular arguments differently, but infrastructure and access to funding would continue to restrict construction. The difficulty of expanding submarine production is tied to both constraints. Large warships had a political advantage in this interpretation: Hitler's attraction to prestigious ships could help the navy compete with Göring's demands for the Luftwaffe. Destroyers and submarines were harder to promote through the same appeal.