Once the live devs moved from the original view of FF as a ranged tanker ( pre-release, bubblers could shoot through PFF, there were 3 small bubbles on 2 minute timers) to FF as a buff set with soft controls, the devs were caught in a bind. In some groups, FF is overpowered in ways no other defender primary is. While, in others, it's underpowered. But the aggregate performance is fine.
Anyway ...
The big thing that rankles me is that Bonfire can use the KB to KD proc and then leverage damage procs for pretty good safety and damage. Meanwhile, Repulsion Field still has, IIRC, an end cost of 1 / mob and can't take KB or damage sets.
Force Bolt could also do with something ... anything ... to make it useful against AVs that tend to be immune to Detention Field, KB, and repel.