Under some circumstances Offense set does more critical damage than CD set

The main problem is that such calculations are pretty hard for applying to the actual combat, especially in PvP. We have buffs and debuffs for CD, CC and Offense which can be freely combined and changed multiple times during single battle.

In general:

CD UP buffs or attacks with internally increased CD increase value of offense mods and decreases value of CD mods.
Offense UP buffs or attacks with internally increased Offense doing the opposite (unless such offense increase is multiplicative).
And debuffs reverse behavior above.

But it's very useful for long fights in the controlled environment (hello raids).