Sch dps question

I think I'm missing something obvious here.

Ruin 2, 100 pot. Broil 230 pot.

If I need to use an ogcd ot seems plain SE wants you to use ruin 2 and weave the ogcd. (Assuming miasma 2 and bio is already up)

But the math doesn't work out. Even if you delay half a gcd, 1.25 sec, on broil to spam an ogcd you still avg 115 potency while ruin 2 is 100 and less mp efficient. (And no ogcd takes a full 1.25 sec anyway)

ie: let's say an ogcd delays my broul by 1.25 sec. I do this twice. I've now spent 2.5 sec on ogcds and 2.5 sec on broil for a total of 230 potency. Let's say those 2 times I delayed broil I used ruin 2 instead. Now I've spent 5 sec on two ruin2 for 200 potency.

So why in the world should I ever use ruin 2 with the only exceptions I see being mobility, or exclusively double weaving as single weaving seems to be a dps loss?

To be honest, Ruin II is a victim of the shared base-class issue that crops up with SCH and SMN. Ruin II is specifically an ARC ability, and it's one that SMN makes use of heavily in its rotation, meaning that it's very useful there (SMN has a lot of oGCDs to weave, and can proc Ruin IV as an upgrade for it). As an ARC ability, however, it's also shared with SCH, which has better direct damage options and better instant-cast options than Ruin II, which means it's nowhere near as useful for SCH. Basically the only time you should be using it is right before a transition phase if you don't have time to cast Broil II. Source.

Ruin II is only good with a double weave. Then it surpasses clipping your broil with a single ogcd. The other scenario is if you're moving and can only ruin II then it doesn't matter if you're weaving or not it's still a gcd you would otherwise sit on.

Another lesser known fact is that the advantage of using cleric stance is lost if you clip your gcd to use it. Only ever weave cleric.

Miasma II is used for weaving over Ruin II, the only time you would ever want to use Ruin II over Miasma II is when you have to move away from the target, or if your are running low on mana.