Like a lot of abilities, Tempered Will used to be far more useful in 1.23 - there it's cooldown time was much less, and coupled with the fact so many mobs used annoying knockback attacks (like plant traps, vultures, boars etc), it was very useful to have. Now, I forget it's even there, as a lot of mobs that used to knockback don't anymore mean it's indeed situational at best.