Keeve:

Given what you say

Here is a general starting rotation:
Bio II+Obey(so the pet starts attacking while you're casting) -> Miasma -> Bio -> Fester during GCD(make sure to delay it a little more until the Bio debuff is present) -> Shadow Flare -> Thunder -> Ruin -> Ruin II -> Raging Strikes+Fester during GCD -> Bio -> Thunder -> Miasma -> Bio II -> Miasma II -> Fester+Rouse During GCD-> Bio -> Contagion+Spur during GCD-> Ruin -> Ruin II -> Enkindle during GCD -> Shadow Flare

Does this apply for long term fights, like bosses or primals?
Or for everything and anything?

Also, excuse my ignorance, but what is the reason and/or benefit or RS+Fester?
I would have "assumed" that before your initial rotation a Raging STrike would be a good idea. Why is it not?