The final verdict: flotilla leader, not admiral

In a few words, how capable was Dönitz?

A good submarine-force leader, but not a good admiral or strategic planner.

The concise verdict is that Dönitz could lead submarine forces but did not demonstrate the ability to step back, assess the larger war, and devise a sound naval strategy. His wolfpack concept relied on an earlier strategy rather than a genuinely new solution. Signals discipline, Allied adaptation, production, and the missed warning before Operation Torch all expose the same limitation. The final distinction is between driving a flotilla hard and directing a navy intelligently.