If you actually think about the examples Yoshida mentioned then you'd see there could be some value in skill speed. Should you stack skill speed on turn 8? Probably not, as you are always on the target doing damage. What about turn 7? There are times when you are aren't using skills, even if only for a second, and skill speed might make up for that down time. In the long run, though, it doesn't matter as the secondary stats are all minimal dps increases.