I wonder if anyone knows this book that I read about 30 (possibly more) years ago: A race of people who have generated large wealth on their planet by running tourist operations on other planets. They fabricate ruins and 'terraform' new worlds to set them up for tourism.
These people see themselves as superior in many ways including physical. The reality is that they are soft and overconfident. An agent of one company visits a planet they are intending to prepare for tourism but discovers indigenous people. He is taken prisoner by the natives but joins their fight against his own people to protect the planet and their survival. The indigenous people with his help discover a super-weapon planetary defense system and destroy the invaders.
My recollection may be flawed, but I think this was the gist of it.
I also remembered that in the story I am looking for, the native people are the (now primitive) decendants of an advanced society that has (somehow) been destroyed.