Most likely its because of using THF as a subjob. I remember a while back SE saying in an interview that they wanted people to experiment with diff subjobs and implied that they didn't want THF to be one of them (mostly due to 2handers using it for SAWS). That coupled with the DNC job being designed to be used primarily as a SJ first is why it has DW tiers at earlier levels.

Because of this, I totally see THF getting DW 3 and 4 the next 2 level increases since it was given DW 1 and 2 on the last 2. Sucks that we have to wait that long, but in the end it will work out.