I think the thought is without the merger there is a deterrent timeline where Boeing maintains enough management competence to not turn development of the 787 into an outsourced/vendor funded cluster fuck. Which might have left them with enough funding to replace the 737 with something modern and safe.

Meaning failure to develop the 787 on time an on budget left them with no time to develop a proper replacement for the 737 without losing customers to the Airbus 320. Seriously it took Boeing about 9 years to develop and deliver the 787.