The idea that tie in books are lesser than others is simply no true.
I never did and never would say that tie-in books, or any work for hire writing, is lesser. Half or more of the stories that inspired me to become a writer when I was a kid were stories written for a pre-existing universe, whether it was Star Trek
or comics or something similar. And that's not even what I'm talking about. Writing stories set in the Star Trek
universe is one thing-- making up a "new" Space Opera series and calling it Star Trek
and naming the captain James Kirk and so forth is quite another. Being inspired by somebody else's concept to create something of your own is great-- using their ideas instead of your own is not great (and by "you" I mean the generic "you").