Guardians, BF, Elder Wraiths' "glitched" KB intentional?

For whatever reason, Brandish hits Elder Wraiths in their invincible frame.

It's because brandish is fast enough that the second hit gets in before the invincibility starts. Then by the time the third hit comes, the wraith is out of invincibility. If you pause between the first and second brandish, the second brandish will miss.