https://www.amazon.com/747-Creating-Worlds-Adventures-Aviati...
OTOH, part of the reason the duopoly persists is because of heavy regulation, and specifically the strict safety regimen. From that angle Boeing has significant economic motivation to promote costly safety margins, particularly those which raise barriers to entry into their markets.
I understand the argument that Boeing employs countless conscientious, professional engineers. But in 2018, with American business culture having internalized decades of cynical, anti-social business practices, I'd be careful about overestimating the influence of the professional class.
Also because Boeing was ultimately more successful than the third competitor in the market. Boeing sold many aircraft during a period in time when the DC-10's reliability was deeply questionable in its early years, due to some aircraft design/engineering related fatalities that killed hundreds of people. There have been a shitload of fatal Boeing accidents including things like the 747-vs-747 crash in the canary islands, a Japanese airline 747 that flew into a mountain, etc, but those were all caused by human factors.
There have been very few large fatality crashes that can be directly traced back to an inherent design flaw in a Boeing plane.
There were several fatal 737 accidents due to uncommanded rudder actuation.
The earlier 707 also had several cashes linked to rudder design and the UK CAA required design changes before it was permitted on the UK register.
I found that odd because, as you say, they certainly have the expertise and track record for seemingly comparable projects. To provide evidence for the hypothesis (which is a larger theme in political economics) it would be interesting to see what the precise engineering and management hurdles were as compared to smaller aircraft, especially the marginal cost. The crux of the hypothesis would be that techniques needed to remain competitive in Boeing's market--e.g. foldable wings--would be regulated in a way that made them especially costly to develop and gain regulatory approval.