The role of McDonnell-Douglas is exaggerated. Boeing had achieved pretty close to a monopoly in the mid-1970s, but things had changed by the mid-1990s. 1. Domestic airlines protected by regulation had been effective monopolies and Boeing's engineer-led culture thrived in an environment where airlines didn't care about costs. But that environment died with airline deregulation in 1978 and an engineer-led culture made…
What's happening to Boeing isn't really remarkable lots of dinosaur conglomerates rise and fall. I'm just a casual follower but it seems their glory days are from the 60s and 70s and they've been coasting along since then.
1971: Will the Last Person Leaving SEATTLE — Turn Out the Lights
I’d argue the 757, 767 and 737 Classic (i.e. -300 to -500), all of which much more 80s than 70s were much more glorious.
And the 90s brought us the 737NG and 777 which continue to carry more than everything else today and for that matter anything else ever, other than maybe the A320ceo.