I think this is a very interesting article. Misguided, but very interesting.
True, it is important to have contrast in a opera, but saying that being bored is necessary is a bit too pessimistic for my tastes.
For me a prime example is Mozart. He contrasts the extremes of comedy and tragedy to keep the viewer interested.
The example given in this article of Die Meistersinger being able to be cut by about an hour is in my view extreme. The production I saw recently at Glyndebourne made the 'unecessary' bits interesting in other ways. It is the job of the director to make the storyline interesting and hold the interest of the viewers in sections such as long recit sections where people's attention might wander.