The passive was only meant to affect Leon. (Passives like from the extra final chapter boss challenges for the power diamonds and the crate boosts are meant to affect everyone).
I could have made the Earthen Blessing skill castable from the menu, but I felt like that would have been a tad bit overpowered at the time of making it since the player could simply cast it once as Leon (or any staff holder), and then walk around to regenerate MP and spam it over and over again since unlike Healiara, it does have a chance to revive all party members at once. Plus the Earthen Blessing state the spell provides grants 10% regeneration to all HP, TP, and MP.