the way i read slash/pierce debuff works is rather than being multiplicative with your modifiers, it simply just means you divide your potency after the modifiers by 0.9 to factor the debuff in the final numbers. so split with gauss would be 140 x 1.638 (229.30), then divided by 0.9 for debuff=254.8 (255 rounded) vs the 252 rounded

stance dancing is manageable, but i've been finding it takes a fair amount of tunnelvision to make sure that head graze/blank also are used in gauss only. im sure if you ignored those oGCDs that the benefit from stance dancing would be pretty small; but working around rico+gr and then those two attacks as well is sort of annoying outside of a dummy fight