Youre probably just us9ng them to late. This game isnt as simple as: hit button+ping=effect starts. Theres an animation delay. You hit the bitton and your xharacter starts doing a buncha flashy bs, at the end of that bs the effect starts. This is most obvious casting aoe heals or shield effects. If you use shale it off, the animation starts (char bound with wires and 'breaks them', and you only get your shield when they break. However the animation then spreads to every9ne around you on a staggered delay. The shield icons and bars will also be staggered because of the animations. Same with aoe heals. Watch the hp bars of a party during an aoe heal. They do not all go up at once. Its staggered.

This means you cant cast shields or heals at the last possoble moment because some or all of the party may not get the effect before they are dead.

This is true for single target actions like mitigation as well. Countless stories of a pld using hallowed ground, the recast timer starts ticking and the pld dies and the ability was used. But they cut it to close so the animation didnt finish therefore the effect didnt start before the hit.

The upside is that the effect starts late, but still lasts the full x seconds. Storms eye buff takes an extra second to apply, but also lasts an extra second at the end when you reapply it.

Tldr: use actions earlier. The effect doesnt start until the animation ends. Actions with longer animations take longer to have an effect (aoe heals/shields for example). Its just how the game is programmed.