Old Design?
2 pence's worth...
Another way of looking at this record is that Boeing have procrastinated too long over replacing such an ancient design. Since the introduction of the A320 Airbus have helped themselves to a very large slice of the market, with Boeing failing to introduce a superior, or even equal, design to compete. Yes, the 737 family's sales figures have been healthy, but really they ought to be regarded as a significant under-performance. Boeing could have preserved their percentage market share of the 1980s, 1970s, but ceded that without much of a fight.
If Boeing had introduced a new design 25, 30 years ago, and made it extremely hard for Airbus to win sales on technical merit alone, we'd now be looking at a very different Boeing to the one we know today. Airbus's unfettered success has been a 30 year indicator that Boeing has needed to do something, and the row over the very effective C Series is an indicator that the writing is being written on the wall.
Boeing can still regain their former leading position, but every A320neo sale that happens now is yet another 737 (or its successor) that isn't sold. Half-baked solutions like 737-MAX simply gives Airbus even longer to make huge money from the A320neo family, and leaves the field open for aircraft like the C series to take a massive slice of the smaller end of the market.