I don't think a 420 gn arrow from a recurve is going to have much trajectory advantage over a 500 gn arrow. It's still going to drop out of the kill zone and wound the animal if the target is beyond 3 yards of your estimate, just like the 500 gn arrow will.

I really hate that version of pro light arrow reasoning anyway. It carries sort of an unethical taint to me, making us sound like we should take shots on game when we're not reasonably certain of the distance.

But, frankly, I'm not concerned about someone hunting with a 420 gn arrow. I've long preached that there should be a 400 gn minimum legal arrow weight for hunting. That goes double for traditional bows, where we're not pumping out gobs and gobs of KE. 420 grains is lighter than I'd use or recommend, but I'm not going to bust some else's chops for using it.