I think the problem could be in the question as most travellers would not care about the percentage, just the nominal delay in minutes of their flight.

If you posed would 70% be a bad percentage then I assume the average man would say that's a bit poor. But if his flight and his future flights were on time I suspect he wouldnt care less that 30% of BA flights left late.

Obviously there is some overlap if a pax sees that figure, that could influence their airline-choice-decision-making but alas....