Okay, I've failed to weigh in on an issue in my wheel house (as a retired JAG officer). There are actually two separate, but related, issues here regarding Bergdahl: 1) unlawful command influence, and b) ability to have a fair trial.
Article 37 is difficult to prove, and disfavored by judges. To my knowledge, it has never been argued regarding the CiC status of the President, but I've not researched the issue specifically. On the other hand, Trump's statements were very specific which is usually required to sustain an article 37 claim, so there is a good deal of merit to that assertion.
With regard to a fair trial, it is a little mushier, because it is fairly easy to assert that an officer (s) was/w ere not influenced by the statements, but, conversely, the criteria are a bit broader for the making a claim.
In combination, though, I think Bergdahl has a surprisingly strong claim.