Using DoT T-2 data we can see how the US airlines actually deploy the 737. Given the MAX issues, it is useful to understand how the 737 actually is put to work.
The first item to consider is how these aircraft are in some ways a work in progress. Take for example the situation at American Airlines. The table lists the average seating for the 737 and competing models at the airline. Only the A319 fleet has had a stable LOPA. We have noted before the airline plans to move the 737-800 seating to match that of the MAX8.