i see your point but Leon and most spell casting monsters already regen MP out of battle, and there are revive and healing spells that are cheaper to cast even all together at once are still less than Earthen Blessing unless your reviving the whole party except for 1 character. plus TP does not carry over between battles nor build up out of battle, and not to mention that there is now gear that provides passives that casting it out of battle less worthwhile as it is a lot of MP invested that as far as i'm currently aware will not regen all the MP used to cast it on most characters (unless they are fairly high leveled or have gear that also gives MP regen).
but yeah it is op to use when i don't feel like using items to restore MP on Characters that Don't have natural MP regen, nor do i wanna swap their gear as i'm admittedly too lazy to shuffle all of their equipment back and forth every few fights just for MP to cast buffs i don't need most fights. and for TP that resets every fight, equipping gear tailored to charge TP during a fight is better than burning 200MP on one character just so the others gain more TP per turn.
but i will admit i did prefer using it to revive party members mid fight as it restored more HP than the springy mushroom and making the potion was resource costly which limited how many i could make per resource run. but now there are better reviving items should the player have the gold to buy them (once they hit Nova or complete the snake den restoration)