The fact that other short-CDs need so much crap stapled onto them speaks to an underlying design issue, and in fact I'd go a step further and say TBN also having Darkside attached also shows the same issue (but on a smaller scale).

In a well-designed combat system, "I block the next 1-2 attacks" or "I got a sizeable HP-shield now" should be more than enough for an ability to be awesome to use. It should not need a lawnmower and a rubber duck stapled bolted on top, too.

Darkside as a whole is frankly a mechanic that is so outdated as a concept ("Please keep up this perfectly static buff with no real resource constraint and no randomized element at all, many skill, such play, so agency, wow"), it ought to be removed whole, anyways. Just increase all potencies by 10%, done. If someone says this'd be somehow inferior, please explain how a trait "Your very first GCD in a fight deals -9% damage" is somehow good design, because that is what Darkside amounts to.