[Note edited for clarity] Pierce determines the steepness of the Accuracy-Damage curve, i.e. how far damage and defense-penetration can vary when going from 0% to 200% Accuracy. Positive piece means the domain has tightened; it takes less than +/- 100% Accuracy, starting from the center of 100%, to reach +/- 100% Damage or Defense. When it's negative (called Spread), it means that neither a full miss nor full defense-penetration is possible. Pierce 50, for instance, would mean that you already miss at anything less than 50% Accuracy and already fully penetrate enemy defenses at just 150% Accuracy. Spread-50 would mean that even at 0% Accuracy, you'd still do 50% damage, but even at 200% Accuracy, you'd only penetrate 50% of the enemy's defense. Thus, Pierce and Spread become a matter of risk-reward mitigation/exploitation. Pierce-75, for instance, will penetrate all enemy Defense with just an Accuracy of 125%, but would also miss entirely with an Accuracy of 75%. Thus, it is most useful when an enemy has set itself up as to be unable to dodge or has become exhausted. A skill with high Spread, on the other hand, could allow you to recoup some damage potential after being completely Blinded. Spread Shot enough and you're bound to hit something (making it pretty situationally useful so long as friendly fire doesn't exist...).
So let's apply this mechanic to two skills: Between the Eyes (MCH), a former PvP skill whose name fits well for how we'll use it below, and Disembowel (DRG), which has a rather unique animation that should offer a good segue to another concept (though one that comes largely free, consequent to the above Accuracy stuff).
Between the Eyes in generally considered an execution skill. You either weary the enemy until its stats are so low it can't possibly contribute significant any net Evasion (a resultant Accuracy of less than 100), so you only have your bonus damage to think about, or you stun it and immediately blast it, to nearly the same effect.
Now, let's say we make more use of our more peculiar animations. Disembowel is more of a 'hybrid' skill; it includes in its animation a sort of forced parry and counterattack, and this sees use in its new effects. For just as an attack has Precision, Evasion within a counterattack not only affects the incoming attack, but also the counterattack's own Precision. In short, the more damage you avoided as a result of Disembowel's Evasion, the more damage Disembowel itself would do.
:: Simply put, we can take that simple underlying mechanic, Accuracy, and draw another mechanic from it (counter-attacks) with ease. Take that meme of, "Don't dodge, just Midare (the animation may go off, but they'll die before the damage can trigger)," and milk it for all its worth. You could then take that further to give obvious reason to use skills with such chunky animations as Power Slash, bringing them back into the arsenal of animations (and matching effects) available to players.
Meanwhile, both Disembowel and Between the Eyes could be horrible choices against a highly-evasive opponent, such that would be better served by using Grenado Shot, Spread Shot, or Split Shot, at ascending risk vs. reward, or Chaos Thrust, Sonic Thrust, Wheeling Thrust, Vorpal Thrust/Fang and Claw, or True Thrust/Full Thrust, again at ascending risk vs. reward.
You can have strong but inaccurate skills, weaker but more accurate skills, and any manner of precise skills (a further advantage when advantaged, and a further disadvantage when disadvantaged), which would fit right in alongside manipulations of enemies and the idea of risk from enemy attacks (including their strong ones that you could usually evade, but not when already exhausted).
Now, all that, of course, would be just a beginning. It's literally one additional effect or element mentioned in a tooltip. But now it involves so much more that's all hugely manipulable, offering huge room for tactics and often even strategy.
How do we deal with this pack of three charging armored lizardkin? We've got a shit party of a WHM, two PLDs, two DRGs, a Bard, a Ninja, and a Machinist. Let them bleed us, getting them worked into a frenzy from bloodlust aggravated by Foe Requiem, get the healer to undo their work all at once so they all -- incredibly pissed -- focus on him, then put a tank wall and our two DRGs in the way at the last second, deflect two and impale the third, and finish him off with our NIN and MCH while he's still stuck there. Now, does that all come down to Accuracy, Stamina, and Pierce? No. But what you'd see on your tooltips would be that last bit, and its gameplay transects the way all interactions would now work (Accuracy) and the core basis of gameplay pace (Stamina), such that its exploitation ends up very, very satisfying.
Add to this a further system within AI, like "Focus", and a Armor-break system (let's just call it "Break") and you can give each skill a place that is created by its surrounding skills and situations. Disembowel doesn't need to arbitrarily nested between True Thrust and Chaos Thrust (accessed, really, only to do the CT-WT-F&C line as a whole); it can have things that inherently feed into and from it, and multiple of them at that.