ok well u are rigth but not 100%, think about this when u make the 60/60/60 lets call this gdk, if u get ur gdk to 60 atk u can us dragon sword for example, and u can get 40 defence first to go to the crab island and use 3-4 crabs spot, this means more xp per h, ok thats with the gdk, but a pure cant have defence or have specefic build, a easy example of this are obbypures, 1/60/1 and lets say 61 ranged just for this example, now where u must us ur math is on the xp/h eac acc has, getting 60/60/60 with gear and pots its less time comsuming that making 1/60/1 60 ranged, gdk will always have a better xp/h rate while the pure will have less
now think about making a 1/75/1 acc, that will take a some time to do and defitly is harder that just make a gdk