I would rather have the entire TH growth mechanism scrapped entirely so that the only TH level applied to the mob is that you get from the thf's TH level rather than have this situation where the entire job class, in party situations, is forced into a single role for the duration of the fight. And really, the affect of higher levels of TH on the mob is insignificant anyway. The problem is player perception that will force thf's to full time gimp gear.
The only people I've ever seen "forcing" THFs to fulltime a Thief's Knife are THFs themselves (usually the ones who aren't very good). Other players expect you to stick your TH7 on the mob, which is reasonable, and beyond that my experience is that anything else is viewed as a bonus. Higher levels of TH ARE fairly insignificant, and that's a pretty widely understood concept by everyone - I really doubt there are lots of people who are complaining to THFs because they aren't fulltiming max TH gear.
There are really only a small number of exceptions where everyone will expect the THF to do whatever they can to focus on maximizing TH level for whatever small benefit that brings. Stuff that takes significant time to farm a pop for (say, Kirin or JoL), have expensive pop items (Faffy, KB), or don't spawn often (Tiamat).
And let's be honest here, although THF can certainly contribute solid damage, if you're really inviting someone to focus on being a physical DD there are better choices than a THF. That's just reality, if you want to be accepted as a pure DD, use a pure DD job. And I say this as someone who plays THF.
Edited, Nov 14th 2012 4:04pm by Anza