I think shooting under 54 on a SSA 54 course is the best way to classify a world class DG course. I think BG is probably a little harder to be a pro (Tiger Woods level). But thats what makes DG better. You really only have to work maybe 8+ years to be a mediocre pro in DG where as in BG you'd have to play hard for about 9+ years. DG is better because if you play with the right people you get to see someone throw a disc the distance of two football fields. Hitting a golf ball that far is seldom amazing.
Seems to me an overlooked part of DG exercise is bending over to pick up thrown discs. It really adds up. I tell friends who don't play DG to drop a quarter on the sidewalk, then bend over, pick it up, and put it back in your pocket. Then repeat that about a hundred times, which is the approximate number of times I pick up a disc when playing three 18-hole rounds. (I think this alone helps trim up my waist each spring.)
But it's throwing that makes us hot, which I presume means it uses a lot of energy and employs almost all parts of our bodies. Then add walking, and we're talking a lot of exercise.
I don't really know whether DG is better exercise than BG, but both are good and a lot more than most people get.