SMN target swap - how many GCDs to break even?

[Judge_Xero]

I'm a bit confused by what Xero put down but I understand the idea of it.

Ideally bane saves you 3 GCDs that are used to apply dots.

Basically, I think what it comes down to is casting DOTs is stronger than casting Ruin. (80 Potency)
Bio - 240 Potency (@18s)
Miasma - 300 Potency (@24s)
Bio 2 - 350 Potency (@30s)

So while you are saving having to cast your Dots by using Bane, that only allows you to cast extra Ruins (3 x Ruin is only 240 Potency VS Fester 300 Potency). Overall the DOT windup is not that bad since Bio is instant Cast and becomes part of the dot ticks before the GCD is over. Even at the full 2.5s GCD you can have all your DOTs running before the second Dot tick (obviously dependant on when the server tick happens).

Hitting 2+ Mobs with Bane is obviously better.

I'm mainly talking about the situations where a single add spawns. You will often see SMN's that will Bane to that mob and then blast it with Fester. Sure it looks cool, but you just lost like 600 Potency worth of damage, to do 300 Potency.

(300+ from Dots ticking, 300 Potency for using Bane which could have been a fester)

You could have easily cast Bio and Ruin II spammed while auto attacking, for more damage in only a few extra seconds + had 2 Aetherflow stacks to Fester something.

You just prorate the tick, so if its 0.5 seconds till GCD from the application you just say its 0.5/3*potency.

This I'm confused about. You get the full potency of a dot tick whether you cast it 2.5s or 0.5s before the server tick happens. There is no prorating.