I don't see anything wrong with what he said. This is the problem baseball faces, not that there is much they can do about it.
Baseball has seen it's best attendance numbers in it's history over the last 11 seasons. Granted, 2007 was the highest attended season at 79M+. Average from 2005-2016 is about 75M, with 2016 being on the lower end at 73.1M.
Baseball attendance from this point in 2016 to this point is 2017 is down a mere 37 people a game. Orioles attendance is actually up.
If the correlation is MLB is boring = lower attendance, then it must have been an utter snooze-fest 25 years ago when attendance was only about 56M, almost 20M less than average of this generation. In an age with limited options for entertainment. No netflix, no social media, no tinder, not everyone had cable, or internet, access to all the games, scores, info, right in the palm of your hand when ever you want it.
Even if you account for 4 less teams in the league back then, the two Florida teams don't draw hardly anyone at all anyway.
Why is attendance down? If it's because baseball is boring, then it's only a handful of people that are getting bored in the short term, while over the long term, more and more people are taking in ball games than ever before. It seems a lot like the value of things like gold, or homes. The big picture of the graph of it's value is always going up, but with slight dips down at times. Only MLB hasn't had a crash, and probably won't.
Manny and Harper both have said people find baseball boring. I'd say they are speaking about a real small segment of fans.