FFZ has an interesting solution, I think.
Instant Death (or petrification or whatnot) is
entirely possible, and it's likely that one or two party members will have access to this ability (sometimes it deals damage even if it doesn't hit,
somtimes, it just doesn't).
However, it's also
very easy to undo, in many cases, easier to undo than it is to do in the first place. Items that undo statuses are not expensive. Being KO'd (at 0 hp, which is different than dead) is something easily remedied.
FFZ also has a clear "normal -> Elite -> Boss" monster hierarchy, and only normal monsters (the majority of mosnters) can be affected by such attacks. And in these situations, while a particular job might not be able to use a given highest-level power against the boss, they do have other alternatives.
Still, a high-level party of a Black Mage, a Dark Knight, and a
Samurai will be cutting normal monsters down like wheat before the thresher, simply by choosing to do so. That's fairly intentional. It helps the high-level characters feel like a badass.
Monsters, of course, gain access to similar abilities, which can make them dangerous, but, again, fixing it is as simple as asking your buddy to not wail on the monsters this turn, but instead revive you. That plays into the Aggressive/Defensive pace of FFZ combat strategies: you need to employ healing and defensive abilities in order to not die, but every additional round adds to the attrition you're facing.