I think Germany's naval strategy in respect to thier surface assets could have been a bit more aggressive.
Instead, they let thier capital ships get cut up a little bit at a time.
Had the DKM Graf Zepplin been finished and complimented as intended, taken to the North Atlantic with the Bismark or Tirpitz and a supporting screen, including U-Boats, there would have been hell to pay, surely.
I'm sure that the Royal Navy would have had to contend with them eventually, perhaps in a scenario like the WWI battle of Jutland, but at least the ships would have been out there doing what they were intended.