I had similar thoughts not long back.
Or - Lock Heal Staves to the ‘healing’ units, let Sages etc. al keep the other staff types for utility.
Making Light tomes boost magic (and reducing their might to compensate) would indirectly buff healer classes like Bishops and Valkyries by increasing the amount they heal and augmenting their staff range.
This does imply that only healer classes will be using Light magic in the first place, but it’s not like Light magic as a weapon type is all that different from Anima.