Well, I just wrote up an actual analysis for the Classy Cane/Pearlwood Sword and Pearlwood Bow, and hilariously enough the latter ended up going up a tier, since unlike some of the other weapons on the list, it has more than zero bossing potential. Just goes to show how strong Ichor Arrows really are. And this means that relative to their respective tiers, the Pearlwood Bow and Rainbow Crystal Staff are equally useful. I might even tilt it slightly in the Pearlwood Bow's favor since the RCS can't even hurt the boss you'd most likely use it against. I dunno, am I biased? I've talked to a few people on Discord who thought the Rainbow Crystal was pretty good, or even better than the Lunar Portal Staff. But based on my testing, I really don't think I'm being unfair to it by assigning it to D- rank.