It depends on who the moat is supposed to keep out. A reasonable case from an antitrust regulator would be that if a provider of models/apis gleans the prompts from the users of the apis to build competing products... they are in trouble.
Good prompts may actually have a moat - a complex agent system is basically just a lot of prompts and infra to co-ordinate the outputs/inputs.
Good prompts may actually have a moat - a complex agent system is basically just a lot of prompts and infra to co-ordinate the outputs/inputs.