I'd move Bowling Green, Grand Rapids and Austin up, definitely. Pittsburgh down. And I'd add Portland, OR to the list -- several top courses in the country in Portland and the scene is growing.
I'm not sure what "Local support" is worth for courses, but that's a place where Bowling Green gains a lot of ground. They don't necessarily have world class courses yet, but they have tremendous volunteer support and good upkeep of all their courses. The same goes for Raleigh -- no true world-class courses, but amazing, amazing course/tourney support.
People will keep making suggestions, so I'd go ahead and bump it to a Top-20 list. And to help get there, I nominate Allentown, PA; Augusta, GA; and Dallas, TX to go on the list.
I would also look at a list of cities that have hosted Pro/Am Worlds tournaments in the past (if you can find one), as that would give you leads to other cities that may have a critical mass of dedicated disc golfers and several decent courses... (Note: not all cities that have hosted worlds have good disc golf scenes -- Houston, for instance).
You'll be hard pressed to find any golfer that has enough knowledge of all the local scenes across the country to make any true hierarchy completely valid, but you should be able to get close -- or you will have to do the slightly more objective thing, come up with a weighted system for each city, score each city in each category, and come up with a hierarchy that way.
If you decide to go the more objective city-scorecard route, I would suggest categories such as (# of holes in a 50 mile radius of the city; # of sanctioned tourneys in a year; # of top-tier courses within 100 miles of the city; accessibility, navigability, helpfulness of the local disc golf Web site; overall course maintenance; extra points for hosting A-tier or higher tourneys; extra points for public/private courses with camping; enthusiasm of the local disc golf scene, etc...) Hard to get definitive measurements of all of these, but it would be a fun project to take on if anyone had the time -- if you want to take it on, I would see if you can pitch it as a story to the fabled Flying Disc Magazine and get some sort of compensation for your time and effort. I think most disc golfers would love to see the results.