I'd suggest buffing the explosion damage to 1x normal swing damage.
Or the slash to 3x normal swing dmg.
That's still only about hitting 2 of the 3 slashes of calibur charge.
(also an aoe size increase for cutter series charges might be justified)
(also ionized salt bomb's inherittent bonus of "damage vs slimes very high" is entirely meaningless)
My Combuster deals quite a lot of damage as-is and I'm fine with doing 300 + 80 + 80 to everything near the front of me. Also being able to throw fire essentially is nice. The Status/Range I think is more than enough to compensate over the Calibur - at least we don't have to subject ourselves to being in a crowd to attack.