Granted, most 737 MAX orders were for larger variants, and also the 737 flies farther (the Embraer is very much more of a regional jet). But there's a lot of routes that could be done using either, and the Embraer wins many of those, even before you consider the fact that the 737 MAX flat-out can't fly them at all since it's grounded indefinitely.
So overall they've got superior competition from Airbus throughout the entire segment, and superior competition from Embraer at the bottom of the segment as well. Boeing is in a rough spot. They should have built a clean sheet redesign of the 737 awhile ago to handle the same segment, but they did not, and now they're really suffering for it.
Now if someone built a plane with the same type certificate required with capacity from 25 to 300 (exact bound are of course negotiable) passengers and can deliver in quantity that would catch South west's attention and probably change their entire fleet. I suspect that isn't possible but...