So I tried using the exp bonus and one account with heirloom gear and the other not, when I turn in the same quests both characters had the same exact exp.
It’s kinda tone deaf. RAF used to be 200%, but that was “too fast” according to Blizz, so they hammered it down to 50% and made it so it wouldn’t stack with heirlooms.
Eh, full heirlooms are expensive if you don’t have any collected, so at least there’s a gap where its useful for people who haven’t got them or the gold.