Unfortunately, doctors are human and can make mistakes. If another doctor is “a friend” of the first doc, I could imagine that this second doc had confidence that the first doc’s opinion was accurate and there was no reason to question the diagnosis. In this field with such difficult work, your story is not uncommon.
It does sound like you found a good surgeon who questions everything (as it should be) and was able to repair the failed first surgery.
Hardware is not absolutely required. Yes- hardware helps to insure that the fusion will be successful but does guarantee fusion. Not using a plate is not malpractice.