I don't think it's fair to say BA are using it as a tool unless or until they are found to have acted unreasonably, whether by employment tribunal or (if it went ahead) arbitration. BA aren't exactly known for capriciously sacking people, there's little reason to believe they haven't scrupulously followed procedure here.
We only know of one that got as far as a tribunal. It upheld the decision. BA's disciplinary procedure has not been an issue for any union before, just the opposite in fact. There is no reason at all to suggest that it is different here.