Stat scaling in weapons

I’ve been recently getting a bunch of weapons that have worse scaling than the one I’ve been using but it’s not making sense to me from a scale of progression. I’ve been using Morgott’s sword on my bleed build since I got it but I just beat Niall and his weapon has worse Dex scaling than a sword I’ve gotten hours ago atp. Am I right to look for letter grades when choosing weapons or is that something I should be looking at loosely?