Bard: Chords of cessation does not slow

[jazzman_so_fresh]

The wiki says it has a 20% slow in addition to its pbaoe dot. I used a stopwatch on a cactus in OT, and I didn't notice a difference. It struck me 11 times in 30 seconds, with and without the song.

Using Largo's binding (30% slow), I measured only 7 strikes in 30s.

Is the game mechanic broken? Can it be fixed? At the very least, I shouldnt receive a "your song didn't take hold" message when the mob is already slowed, because that song's slow component is zero (no conflict)