Simply annunciating 'RadAlt Mismatch' would have caught the error upstream both systems-wise and human cognition-wise.
Unfortunately most pilots do not have instant recall of the connection between complex systems. Especially during what seems to have been a somewhat stressed approach. Bringing attention to an apparently irrelevant fault (though we now know there is a connection) would only serve to add confusion to an already difficult situation.
I suggest that a radalt warning would not lead to the crew thinking "that's why we got the gear warning and we must be aware that the autothrottle might retard." More likely would be "what the **** is that about?" and distract them from the real danger.