Honnestly I wouldn't go as far as claim THF=/THF. TH6 is clearly superior to TH2 when farming common drop items ( typically your favorite abyssea pop item), not that it matters a lot since AH is flooded, but anyway. In dynamis I get almost the same amunt of coins each times ( same camps, same set up), and the two times I forgot to change my mule job to THF we got -20% coins ( 200 instead of 250); not a lot of difference indeed. I have many reason to bring THF over /THF, but camate confirms that THF is nothing more than a TH robot. Give me a reason to come back to event as THF main, I used to loveTHF! Or at least reasons to equip my THF mule with something else than Thief knife, armlets, boots, a boomerang and lv 90, and try to meree.
The otherday I was killing tahrongi T3 VNM for the epeen evasion legs. Blu proced right away, could have killed it in 5 minutes, but since I lost claim on the 2 previous ones, I decided to proc TH10 on it with my gimp mule ( again, only TK, AA, feet, range lol) through SA and TA. Took literally 30 minute to get TH9 ( I know since protect wor off at TH9 msg). The next group wanting to pop it was so mad, and I understand. I have many examples with NQ behemoths, taking 30mn to proc TH10 when there is another group( usually 5 THF 1 RDM) waiting to pop.
TH 9 or 10 is something they invented to piss of the player. Th8 is relatively fast to get ( 2- 3 SA and TAs) , but im not really sure if its much better than TH6, and beyond that is rediculously long for such a small improvement.