I think that you are correct, and the committee is going to great lengths to conceal it. I think that the truth will eventually be known, but I doubt that these hearings produce it.
Since nobody claims to know who the whistelblower is, this is just a question to find out who all might have information about the call. Especially, since Vindmann claims the person he spoke to had "a need to know", there's possibility he might know more.
The GOP should quit treating Ciaramella as though he is the whistleblower, and treat him as though he's just another possible witness.