Why HP healing, MP recovery and percentage healing behave differently.
The Heal handler applies the target's healing effectiveness and caps recovery at missing recoverable HP. A stronger weapon cannot recover HP beyond that cap. Exact healing also depends on the skill and its fixed or scaling effect type.
ManaHeal starts from the effect's power, applies the recipient's mana-charge modifier for non-static skills and caps recovery at missing recoverable MP. This handler does not add the caster's M.Atk or a Spiritshot damage multiplier. Check the actual skill effect rather than reuse the spell-damage formula.
HealPercent calculates a percentage of the target's maximum HP, then caps it at missing recoverable HP. This is a different effect from an ordinary scaling heal.