I dunno, 8x damage is what?, 15grs?, I doubt it needs that much, maybe 4x at most imo. What is though is the combination of items, where as toughness is a huge issue for pure foth.
HF survives due to how you can fit stone gauntlets into the build (or at higher level massive amounts of armor from paragon). But foth doesn’t have that luxery, it relies on khasset’s for increased damage.
Maybe tinkering with khassets to gain wrath reduction for all, just to have it working with captain crimson, then adding a higher modifier on khassets for that extra damage. Let’s say the belt now gives 600-700% increased foth damage.
Also, maybe not for just this set, but others who can utilize the belt to gain some extra toughness further down the line.