You may well be able to improve the set up of the Giant, but what struck me when you said it would have been more fun to have been riding a Hahanna was that you were riding on your own. You said it was fast but boring, but what if you had been on your Hahanna and riding with a group on modern FS bikes? You would have got left behind, and that's also boring.
I can't speak for long-travel FS, but my Rocky Mountain is light, roughly as fast as a hardtail up hills (faster up some, if the surface is loose or bumpy) and obviously faster downhill. Overall it's my fastest bike, and the more miles I'm going to cover in the day the more of an advantage it is.