whm weaving

[Zyneste]

Erm, No.

First of all, as a sch you shouldn't be considering using ruin II (that has 200 potency) as a weaving option for single weaves (only double weaves). And that's while considering that their alternative (Broil III) is 280 pot. What you're suggesting is using a 120 potency skill to weave when the alternative is a 300 potency Glare. Don't do it. You will loose more DPS than by just clipping your GCD with glare + ogcd. And you also can't count the tick towards your dps if you're overwriting an existing dot (since those would have ticked anyways)
If you can't cast anything because of movement then yes Dia spam is an actual option. But it does not work as a general weaving tool.

Dia is 120 base potency, 60 per tick. The Potency of Glare is 300 or 120 PPS. This means that for Every second clipping the GCD and not casting Glare you are losing 120 potency.

Overwriting Dia, 3 seconds in to weave a GCD is the same potency as having clipped your GCD to Glare + Mobility. 120 + 60 + 120. Double weaving it, you net a DPS gain over clipping the GCD of 120 potency.

Overwriting Dia, at 9 seconds is a complete DPS gain over Glare. 300 + the additional effects of SpS. Anything weaved with it is also an additional gain.

You do count the ticks that happened before the clip. The damage happened. You don't count the ticks that didn't happen.