Who's to blame?
It's easy to blame Muilenburg, since he isn't the biggest culprit on this max fiasco. Not absolving him, but (he was at least negligent) it just happened that all the Jenga collapsed under his watch.
For sure Calhoun didn't criticise Mcnerney, who is the real father of this Frankenmax 737 fiasco. Nor I think he would have the guts to do it, as it would be akin to taking responsibility for himself as a board member who greenlighted such a terrible idea instead of developing a new single aisle plane.