Why Graf Zeppelin changes British choices too

Would Graf Zeppelin have been decisive if Germany had put the carrier to sea?

It could create problems, but any claim that it would be decisive has to account for how Britain would respond to the new threat.

A German carrier could create problems, and British forces could make mistakes or fall into traps. The counterfactual becomes implausible when Britain makes no adjustment after repeated evidence of the carrier threat. The new capability changes the choices available to both sides. Any assessment of Graf Zeppelin therefore has to account for German action and British adaptation.