The GOPe is claiming, despite Rule 42, that there are no rules. That would mean anything goes, even if someone goes into the convention with a majority of the delegates. This is much bigger than Trump or Cruz or Kasich. It's the GOPe claiming that it picks the nominee, not the voters or the delegates.
No, no, no and no. What they are saying is that the delegates to this Convention make the rules and are not bound by the rules of the last convention.
If, as I expect, Trump arrives at the Convention with a majority of the delegates, the issue will be moot, but what the GOPe is claiming is simply not what you say they are claiming.