The one big advantage for the accused in an Art 32 is that they can get into the prosecutions stuff before the actual trial.....discover, data, witnesses, etc.
If there's not much of a case, then the Art 32 is duty bound to report that to higher.
If it goes forward to a court martial, that normally means the evidence is almost certainly going to be difficult for the accused.
I always was told that if you get in trouble and you're offered an Article 15, take it. Because if the military goes to the trouble of a courts-martial it means they got you.
And I think you are right about the access of the evidence. From what I have read about Grand Juries, only the prosecution presents evidence, the defense does not participate. I had a very good friend of mine who was a Jag and defense attorney. He said he would rather argue for the defense in a military trial than a civilian trial because the rules of evidence are more favorable for the accused in a military trial.
Most informative, thanks for posting this info.