What, exactly, is the use of an "A of A DISAGREE" with no A of A indication to back it up? I can't see it tells you anything useful at all, in fact it merely adds an unquantifiable and unanswerable question into the mix. Had it been fitted it would have required a QRH action to go with it. What could tgat possibly tell you to do about it?
Add another A of A sensor and a triage system and it becomes another matter of course, but it seems unnecessarily harsh to criticise Boeing for not incorporating procedures that can only confuse and not help.