Ruin II should replace Ruin I, but Broil should stay the same.
Ruin II is an instant spell from Arcanist, and Broil is a casting spell from Scholar.
It's not the same thing at all (even with the animation).
Regarding the situation, if you have already put Bio and Miasma and if you have nothing else to instant cast, then Ruin II is the only thing left.