That’s true. I have read same books of Newport and I thought they could be summarized on two pages probably. But I guess that applies to most self help authors. Their whole life work can usually be summarized on a few pages.
As for avoiding the plague that is the filler books, a robust solution is to pick books that have stood the test of time. Hard to beat that strategy. At least that's how I roll. The onus is us, as the reader, to be ruthless about picking the books that truly deserve our attention.