Here you go, two 30s rotations identical in potency. The 0p Succor costs the same. -290 potency. Dot or no dot.
https://i.imgur.com/SYiORgC.png
I think the image above should be clear enough, so feel free to ignore the posts above.
The value of a GCD is the total potency of that GCD. It doesn't matter if it's over time or not. Condense any dot you have into a nuke with a cooldown like in the image above. If you have a 2.5s gap (Succor or doing nothing), the cost of that gap is the same. Having a dot is not more forgiving.
Extend this to multiple dots if you want, the result is the same. The 2.5s gap costs you the potency of your filler.