Hidden OPness of The Dark Seal (no pun intended)

Recently played ranked game in which a player bought a Corrupting Potion and four The Dark Seal(s).

This might seem troll, but The Dark Seal has these stats: +15 AP +100 Mana and the hidden secret, +25% Increased Healing from Potions.

Since a Corrupting Potion is a potion (lol), with four Dark Seals you have effectively doubled the base heal/mana regen.

This means you restore 250 hp, 150 mana per use. At three uses, this is 750 hp and 450 mana. Not to mention a fifth The Dark Seal could be boughten, as well as runes/masteries that increase self healing. I don't really want to do exact numbers, but I'm pretty sure this means a player could have approx. 1500 hp and 750ish mana sitting in their pocket.

Please make the "+25% Increased Healing from Potions" a Unique Passive.