???/thiefFollow

Hey all,
I wanna lvl Thief cause i was farming already for a while on different items with my whm50.
I heard that when you reach thf lvl15 you get an ability that drop rate becomes better. Now comes the thing i wanna ask.
When i reach lvl 25thf and i set it up as Subjob for my whm (whm/thf) for solo farm battles, is the droprate from items then still better or do you really need to have thf as main for better item droprate?

TH1 and TH2 have fairly decent enhancements in drop rates. Soling as pld as opposed to thief has shown me this.

But Thief Knife and AF2 hands are what many people say have negligible drop rates.