will counters magic damage totaly, fortification doesnt counter physical damage, because of the combat passive. Even though im a healer, im still wearing plate so my passive magic defense is crappy and still when i turn on energy shield, most magic damage users see that they cant burst you down and start panicing, because their cooldowns are off for a while. Where as the only counter to the combat passive is to use the lvl 50 fortification ability at the right spot but during that time you cant do anything. (not to mention that you can cc break spears with will, while you cant cc break the Knockdown from combat)
Of course im able to block just fine as well but i was actually writing when i get jumped on. And if you get jumped on you wont survive for long as well. Its not something that happens regularly but it CAN happen.
In theory, Will should counter, but on the battlefield it's another matter. If you're staying alive it's because of Devotion, not because of Will, simply because, unlike melee builds that keep you stunlock and stop you from healing, magic builds give you a bigger margin of time to heal yourself.
The stun/paralysis purge seems great and all, but the impale from death is instant, and so is chain lightning. Unless you know it's coming and pop it beforehand, which is difficult to predict since you can't tell the person build on first glance, there's nearly no chances of you purging the paralysis before the other guy use chain lightning. Unless he gets greedy and use something like the crows first. Plus this skill has 45s CD, which is twice the CD of CCs.
If the other player is smart he will also silence first, which ruins all your plans since the silence immunity from Will doesn't purge it. Only worthwile spells are the magic shield, sadly with a very short duration, and the very last skill of Will that fully negates magic spells. Although i'm unsure if they fixed and made CCs not go through it (otherwise it's easy to cancel it lul).