The problem isn't so much a tier issue. It's that no one likes it when the FB kills his entire party. Or falls down a pit and wastes a rage/frenzy because he took falling damage. Or you need a cleric/wizard to prepare spells purposefully to deal with the FB. You could hope to use marbles. Assuming they don't scatter when the FB falls. Or that you can find a level surface to arrange your marbles on given the technology level of the world.
Yea, you can cheese your way around it by going exalted with Righteous Wrath or by picking up Thayan Knight. But, yea, FB is one of those things I feel is written more for the GM than the PCs.
Personally, I don't have a problem with it. Good on old Ole Killpersonsen that he can be such a force of destruction!
OTOH, I have seen many more PCs nuked by friendly fire in the form of mis-targeted AoE spells, spells with incorrectly calculated AoEs, spells cast in areas where magic was strongly affected by forces of chaos, and other mystic calamities than by martial PCs running amok.