Strategic costs of a submarine-only German fleet

What wider strategic consequences would follow if Germany built a submarine-focused fleet with no battleships or cruisers?

Britain could concentrate more capital ships and carriers against Italy, Germany would struggle to invade Norway or threaten Britain, and destroyer design would lose its large surface ships as a central mission.

Naval force structure affects alliances, campaigns, and the design of supporting ships. Without German capital ships, Italy could face much more of the Royal Navy, while the Norwegian campaign and Operation Sea Lion become harder to imagine. Germany would also have to decide whether its destroyers were coastal craft, cruiser substitutes, or transports for an improvised Norwegian operation. Submarine tonnage therefore could not be increased in isolation from the rest of the fleet.