I'm not sure this is the best fix. Skillchains shouldn't be entirely about magic bursts. Even in the past if a party didn't have a BLM we would still SC, because the added damage was beneficial. It seems a bit silly to make SCs rely on MB to become useful again.
Not every group has BLMs. Though they are admittedly more common since they are needed for grellow, they shouldn't be required to make a battle mechanic useful.

Why not boost SC damage as well? Or maybe give them additional status effects like FFXIV does?