Fester is going to be hitting around 640, perhaps a little more in full darklight, every 20 seconds. You can raging strikes all your numbers if you really want, but its still absurd as raging strikes will give about 50 more damage every 3 seconds on dots to around 380 non-crit. Its also on a 3min cooldown timer.

In order to keep 4 dots up, you have to spend 10 (essentially) seconds in a rotation to keep it up. Discounting garuda pet for a moment, the beginning you'll have a easy time spamming fester and ruin, however as you essentially have 4 dots that you'll have to maintain every 18, 18, 24 and 30 seconds, at most you'll have potentially three, realistically two ruins inbetween updating dots. This doesn't include things like fester, aetherflow, or energy drain which do take some time to activate even though there isn't a GCD associated with it.

Shadowflare is about 55 per 3 seconds. And parsing ifrit will get you 55 average.

Ruin is hitting about 171 give or take.