Actually I would say the prequels had better plots than the OT. It's just that the acting and dialogue are so bad, it's hard to see thru it.
I wouldn't call Lord of the Rings deep, or any more deep than A New Hope or Empire (ie, none of them are really "deep"). Citizen Kane is deep. Lord of the Rings, Star Wars, and Empire are not.
The problem with that is that Power Rangers, Ninja Turtles, or Mickey Mouse were never quality in the same sense that Star Wars or Empire were. To compare them to that is silly. I don't ever recall Power Rangers, Ninja Turtles or Micky Mouse being nominated for an academy award for best picture.
So Star Wars has been more, so it should be more. You can have a big blockbuster family film, and at the same time it can work on another level as a high quality film (like Star Wars, ET, Empire, the Dark Knight, Raiders, Fury Road, etc).
Never lower your standards.