There is no doubt that BFT is one of the worst picks in the game because (1) it is a cost-inefficient unit in general and (2) there is a better&cheaper analogue in the same roster.
Basically, the normal FT ($650) is outperforming BFT in most scenarios despite being $200 cheaper.
The main question here is "How can BFT be improved in order to become an unique unit?"
Well, from what I know the difference between FT and BFT is that the latter is enchanted in some way so...
Let BFT apply some "magical" debuff on contact.
Be it a DOT effect similar to skaven Poisoned Wind debuff or Blinded!
(-27MD -26MA) similar to Solar Bastiladon.
In that way the BFT unit can get its unique feature that would differ it from the cheaper analogue as well as make it cost-efficient.