What? No. That's just a rumor. I've never heard of anyone getting an actual copy as a drop.I am pretty sure you're misunderstanding what that says. I'm am quite confident to say that he meant 250 AP to farm from Nike's Rampage for example, for materials. Nowhere does he say that you should farm Vine fight itself...
You used to be able to buy the last copy, but for some reason, you can't anymore. We don't really know was it a bug that you were able to, or is it a bug that you can't anymore.Vine is always good if you can only reach 40% Def down with your team. Dartagnan's HP Relic weapon doesn't really solve that, mostly because it's HP instead of Elemental attack. Thunder is shoehorned into it due to lack of debuffs on Hime and the synergy with Mammon.
As time passes, we'll get more and more access to C frames, Element resist- and Weapon/Eidolon Def down effects. That means that eventually, we won't need to rely on Vine anymore. Until then... Vine is amazing.
The biggest change is probably Hercules' Relic weapons, as both of them apply a whopping -25%. Combined with her buffs which make her decent overall as well, there's few reasons to use other Souls afterwards.