The Max was developed under James McNerney who is an MBA with no engineering background.
You can argue all you want about who shoulders more responsibility, but Muilenberg was an executive throughout the entire program, and more importantly, was the CEO who oversaw the decision for the certification of the MAX prior to first flight, which was the critically faulty decision.
Though of course he would have had the knowledge to understand something didn’t smell quite right after. Whether he had the sole authority to order a delay or redesign in the intervening time is questionable. It may have been that he couldn’t wrangle enough support from the board to do something dramatic.