Well, the comparison is more apt than you think. The opponents of the kingfish closures said basically the same thing at the time. Not enough data, no reliable data, hidden agendas. I found the NMFS scientists involved to be conscientious, the data to be diligently calculated and supportive of the closure, but not perfect (is it ever, in any endeavor?), and their motives solely the welfare and sustainability of the fish. Yes, the economic impact on the fishing industry was not in their calculus, but it was not supposed to be. Those interests were heard in court, which ruled for the NMFS in the end. Full disclosure, I was the assistant U.S. Attorney who represented the agency against commercial and sportfishing suits to enjoin the closure.
I am not surprised that data on harvest of hogfish is not extensive. For kingfish, the NMFS had observers on commercial vessels and some decent real-time tracking of a large part of the harvest and its decline over the years. Spearing of hogfish is much more diffused. Who is going to monitor every private dock, public boat ramp, marina, dive boat, snorkeler, etc. looking for hogfish? You are just not going to have as extensive a data set. So, I agree that calculating protective measures for hogfish are significantly more subject to estimation as opposed to "precise" calculation. That being said, if they are acting on the best data available then I give them the benefit of the doubt.
Anti-government passion is often shown on this board. I offer you a real-world example based on direct observation of the agency in action, and it was an example of conscientious people, using the information at their disposal (which, by the way, is far more information than their critics can bring to bear), attempting to protect a fishery for the continued and future enjoyment of all. More important, it was a success in every objective term, ultimately for all users of the resource.
You ask, why should we "trust" them. I might ask, why should we not? You claim they don't have much date, but they have more data and a bigger picture than any individual or interest group. Their actions and data are public and subject to review and public comment. No one has pointed out some agenda on their part other than sustaining the species.
Finally, I believe anyone diving since the 70s, being objective, cannot doubt that hogfish are much less numerous and much smaller than ever around South Florida. Is this "scientific?", Well, I don't know (but observation is part of science, too). In any case, my observation of the situation supports protective measures and I am willing to rely on people who do this full time and have much more data than I to determine the degree of protection needed, expecially when their actions are open to the public.