IMO GFs are a sort of trophy. Rarity draws are important for normal cards to help fill out very specific gaps in peoples' decks which is necessary for competition.
But I don't think rarity draws should apply to GFs. Keep them random and keep them special.
While I agree in one respect, I also wonder if the reasoning behind this is to do with GF frays in the brawls. These frays are hard enough to fill as it is, then with some of the soulbounds being such big game changers you can be at a huge disadvantage without them and you can't even rent them. It's hard enough getting GF gladiators as it is.