A German fleet aimed at France and Russia still alarms Britain

How would naval building change if Imperial Germany aimed only for a fleet able to challenge France in the Atlantic and Russia in the Baltic?

Very little; a fleet strong enough for both tasks would still resemble the historical German program and would still draw a Royal Navy response.

Capability matters more here than declared intent. A fleet able to challenge both the French Atlantic Fleet and the Russian Baltic Fleet would surpass either rival and become the next major naval power. Britain would therefore treat it as a new competitor regardless of the rationale offered in Berlin. The resulting programs would look much like the historical arms race because the practical balance of power has barely changed.