The only problem I can see is that having some items that only drop from mobs (diremite web, as an infamous example) is supposed to be the way for combat classes to have access to the economy. If they aren't gathering or crafting, they can still make money by spending time farming web or fleece or whatever.

Having a Gatherer class that can outcompete them in that field would then completely cut those players out of the loop altogether - they'd have practically no way to make money, other than being forced to craft or gather which they may not enjoy.