in my opinion (it’s important that bit)…
GT red is easier physically than Dalby red. Dalby is much longer. I would say that GT is harder technically though. Nothing individually is harder but there is more hard stuff on the trail.
GT black is much longer than Dalby black. There are some tricky bits on both. If you are ok at Dalby then you’ll be ok at GT. The harder bits are dead obvious so you won’t find yourself faced with an impossible obstacle . The route is longer but there are plenty of escape options.
As on the other thread, don’t assume you have to ride all of one loopp. The trails at GT seem to link up much better and the best ride is a mixture of black red and blue.