Well, I don't know most of the individuals currently involved in running the museum so I guess I can't really comment. But I would gently point out that fundamentally, the job of the NRM's staff is to run a museum. It's no good putting expert railway enthuasists in charge if they don't know how to run a museum. The specialist railway knowledge is provided by the museum's curators - that's literally their job - and as far as I can tell, the present curators are good people who know their stuff (e.g. Anthony Coulls). But a museum needs a wide variety of specialist skills, e.g. visitor engagement, education, exhibition design, etc. - not to mention some business-savvy managers at the top to keep an eye on the bottom line (which, even with the benefit of public subsidy, no institution can afford to ignore). For those roles, having the right skillset is far more important than having specialist knowledge of railways.