Provide a detailed and clear description of feature or change that you want to offer.
Angel's Blessing - vulnerable to fire damage. Like a moth on fire or Icarus on the Sun. Actually that spellstone is pretty useful in Nether landscapes so why not nerf that a little just like this. So players needs to be more careful here (especially on Basalt Deltas).
Will of the Ocean - vulnerable out of water. So players wouldn't wanna use it on dry land or they needs to be careful if they want to use a water bucket exploit with this.
Blazing Core - vulnerable in water. Like an opposite to Will of the Ocean. Fire is actually often referenced like opposite to water. So players wouldn't wanna use it underwater or they needs to be careful if they want to free walk on magma blocks underwater.

Describe why you want this. If there's a reason.
It would be fair, since there is already one on Heart of the Golem.

I guess it also will be good for Will of the Ocean to negate vulnerability (partially at least) by rain.