Cleaves, Tailswipes, Movement (Since most of your skills have a cast time, high movement fights negatively impact your damage in ways that don't affect Monks and Dragoons as much) and any fight with plume / targeted aoe mechanics means you're just another body and another change that the tank will have to move, which is usually a no-no. Now, naturally if none of those things is an issue you can replace any Ruin/Ruin II with Miasma II but it seems silly to have to say that.

I did have a question though, I was wondering why open with Bio II over Miasma. Is it a preference thing, or do the number synch up better?