Obviously over a fight you're going to be juggling a lot more than just CS and DS, so the discrepancy between the two values will narrow severely to the point where RNG over multiple fights will blanket any DPS increase or loss, and as such you're really talking about something insignificant in the long run. DS's eCD will increase or decrease by small variations, and CS's eCD will jump up to around 5 seconds(with shorter fight lengths, slightly less). The overall damage of the two abilities will be fairly close, and DS will only jump up if you get some really, really good RNG (so good that it won't normalize to ~6 seconds over the fight duration which is pretty rare except for those ridiculous fight lengths such as 1:40 H:Marrowgar's, etc).