There can be abuse on both sides. An applicant may file an extremely broad application which, to use your term, is a fishing trip and requires the government to allocate resources to respond to that request.
According to the witnesses who appeared earlier, members of the public may have difficulty defining the parameters of their requests. That's absolutely true. Conceptually, I don't see any problem in asking individuals to specify their demands, insofar as they can, which isn't always the case. There must be good faith on both sides. The commissioner must also review whether people acted in good faith in defining the scope of their requests and the government's response.