Shockwave and Aerial Slash should have shorter recast time than actual attack so your garuda dps should increased by those skills. During raging strikes you should use 2 festers + energy drain in case you will need mana later. By gcd i mean that you should time more your festers during you apply bio like in 1:06 you use fester and bio have 6 sec time left. You could wait that 6 sec and then use bio + fester at same time. And i never seen that kind of opener you use bio -> rouse -> spur -> miasma. You can use those abilities as off globals between instant casts.