If you watch broadcast TV on a regular basis, you get to know the times when it's going to be decent and the times when you might find nothing remotely interesting. It's all on a schedule, and that schedule puts better and more expensive entertainment at a time when more people will be watching.

I would say your complaint about quality shows as a percentage of broadcast time is a valid argument for moving TV to more on-demand media (watching a show on Netflix or Hulu vs being on the couch at 9PM on a Thursday). There's still some decent stuff out there. The only thing this doesn't solve is sports programming, which is practically worthless if it's not live and from which NBC makes a fortune as a "premium" football channel.