It does not matter if it is a big X over half the screen or whatever it is, thete is a visual clue. Only it is not wort to be mentioned as contributing factor, and it was recognized.
We can turn in circles a hundred more times but it does not change any fundamentals. The pilots recognized the unavailability of information of the speed information. What they did not due is to follow with the appropriate actions.
We can discuss other visual clues, change the whole architecture of the flight deck, change the logic of the FBW system, add tactile clues, whatever.
In the end it has no effect as all these things still require the crew in charge to take the correct action to fly the aircraft. And that is what really was missing. To consequently think that the pilot is not the final authority and needs to be having the necessary education to do so in the end means to have the fully automatic aircraft.
We can only speculate on the nature of thinking wich lead to the inapropriate actions during the event. The way leading to those however are also cultural, but to understand this you must have lived in France as a foreigner.
In my opinion the real cause of this event lays very deep in the french way of doing things and no amount of changes on the technical side will change this and prevent such or similar events to happen again. We have hammered on Asian crews for causing loss of life on cultural factors but we fail to accept this as a reason for a 'western' crew.