I make sure to wait a second to hit fester after Bio since it has that slower application.
I was under the impression that a contagioned Miasma2 comes out to the same potency as a Ruin3? Either way, I intend to swap Miasma2+contagion for Ruin3 once I swap in Ifrit. I'm aware of the loss of DPS when using SF instead of Ruin3, the idea I had was to use SwiftCast before going into DWT as to have the buffed ShadowFlare replace the Ruin2 that I've usually seen in some openers used as a weave. Its the R2 I'd be replacing, and not a R3.
If its not optimal, then its not optimal. I just don't have the means to test this out.