Tempered Will is a specially egregious ability because for the most part anytime you'd want to use it you can simply, well, not use it, by dodging whatever knockback is coming. If the anti-knockback ability was removed entirely and replaced with a 300 TP restore you'd see that skill suddenly jump from "why even have it on my hotbars" to pretty damn good. The only times I've used it in 3.0 are so I can look cool not getting knocked back by Pillars of Heaven in Ravana, and the last time I used it before that was so I could be lazy and not dodge a divebomb in T13.