@Solipsist depends. let's take poison for instance. id defence is covering everything from physical resistance to magic and ailment resistance, then it would probably be key to taking less damage, however in most rpgs I played, well... all that i can remember, something like poison was a stat check to see if you were poisoned, but if you got poisoned you took full damage. there also is no obvious hp stat, so either that got raised by strength, defense, or it doesn't get raised.
now, as a character who SHOULD be in the middle of it, you need to live though the attacks, defense is obvious.
as a caster or healer who should be in range for the heal but out of range for everything else, evasion makes more sense.
for a manga example, took at tanaka the wizard's dragon fight, me and my friend will joke when we play games that I have mana you aint dying, because that's realistically what the cleric in the game is, if it has mana you aren't going to die. here is the big difference though, in a good number of tabletop games, you roll to see if you screw up or if you crit, with a high enough evasion, you realistically cant get hit by nearly anything else while with defense, you are getting hit all the time, its just a matter of how sever the damage is. in fact, if memory serves, d&d's defense system, at least though ad&d acted more like evasion then defense where you would just not get hit if your defense was high enough.
I think i'm losing the topic a bit, tldr unless mc purposefully goes after something way above his pay grade, he should realistically never get hit, and as long as poison/ailments does not instantly kill, he has mana to stay alive.