I have played Heathland many times, and always enjoy it. I agree with you with the concept that there are very good golf courses at MB that get either lost in the shuffle, or discounted due to the negative connotation to some of MB golf.
Heathland is a very good golf course, and especially in a resort setting containing the other two Legends courses. Heathland is the clear best of the three (with Parkland a bit too easy, and Moorland just a mess), and a solid favorite of mine. I would put it in the top 20 at MB at worst.
That said, I do NOT think it is a "great" golf course, or that it would be considered to be the best in any state (including TN) if it were taken out of MB. While Heathland is both fun and somewhat challenging, and isn't gimmicky in the least, it lacks something. What that something is, is tough for me to quantify, but The Love Course, Tiger's Eye, Caledonia, True Blue, Tidewater and others just in the MB area have more of whatever stirs the soul of a golfer and make you want to play a course again immediately. I just don't leave Heathland with that feeling; once a summer is fine.