I do think he's right that baseball isn't complex but his reasons for believing that are stupid. I mean, if you compare to football, there are some huge uneducated morons who score <10 on the Wonderlic and they still can memorize whole NFL playbooks and not f*** it up that much. When you dedicate your whole life to a sport with set rules, pretty much anyone can understand how to play. Baseball is even simpler for a player because there is hardly any true decision making when you play. 95%+ of the time, there is one correct play and you go your whole life repeating that and it's as automatic as can be.
From a manager perspective, aside from playing match-ups and defensive positioning (both which are better handled by the analytics team anyway and the manager is just the messenger), there's not a heck of a lot beyond sending out your best players as often as you can. I think the best manager in baseball is one who works effectively with the analytics team and employ's strategy based on that (and relying less on hunch and instinct), but also has really strong soft skills to manage ego's, give bad news, motivate the team, etc. I'm not sure that's still a good idea to put a rookie manager right into the MLB like the Marlins, but if there's ever a sport you could get away with that, it's baseball.