[Suspicious]

Well, here's another few reasons why this 'phenomenon' is the case:

1) You can count on one hand the number of monsters that roll higher RES than DEF. Also the majority of monsters that have higher RES than DEF also have excellent CEL/LUC.

2) RES doesn't goddamn matter because Charge Mind makes RES pitifully ineffective (2.5xmore damage - RES) unless you have Body Guard/Wraithguard (which monsters don't have). There's also no enemies out there that have effects that straight up negate magic (think Nullstone Gauntlets), and no enemy that can competently absorb burst (looking at you, useless Sturdy prefix...)

3) There is not a single enemy outside of the arena that can inflict Silence, or inflict Silence so fast that the mage cannot get off both Charge Mind and a spell. Also, the availability of silence counters (Throatopener, Silent Prayer, etc) render Silence moot.

4) Elemental immunities/heavy resists don't actually pose a problem. Casters usually have astronomically high WIL and multiple skill slots (even before the change that made levels give skill slots), so if they packed fire against fire resistant enemies, they most certainly packed wind, earth, and ice, too.