Muilenburg isn't completely blameless, but dumping this on him is rather unfair. When he became CEO in 2015, the MAX was already well along the development cycle, and more importantly he inherited twenty years of culture and communication problems that Condit started, and Stonecipher reinforced. Condit set in place a culture of questionable ethics and a "shoot the messenger" mentality that crippled the ability to communicate issues up the management ladder - and he did it amazingly quickly. The 'shoot the messenger' mentality was a huge part of the 787 train wreck - and even infected the 747-8 program. First hand knowledge on the 747-8 - we had a good chief engineer that I respected and that listened. He came to me at one point - noting that my system was on the critical path for first flight - and if I needed more resources to tell him and he'd make sure I got whatever I needed. But he made the mistake of telling the higher ups that we were behind schedule, resulting in his being demoted and replaced with someone from Long Beach who told the higher ups what they wanted to hear (and promptly blessed a cut my headcount). Of course that didn't help our schedule issues which got way worse with the new chief engineer...
I was actually seeing some signs of things getting better in the year after Muilenburg become CEO before I retired, but it may have been too late to prevent the problems with the MAX.