Bosses shouldn't have 80% resistance to the school they're in.
I'm an Ice Student and have been fighting Jacques the Scratcher 5 times now, and it's getting really annoying.
Just use an Ice Prism treasure card before each attack and you won't have a problem with him. There may be some at the Bazaar, or ask a high level friend to buy a few from a treasure card vendor and trade them to you.
Actually, there are a few options on the table. Have you tried them?
If you have to hit him with Ice school, you might consider using an Ice Prism to convert your damage to fire.
Alternatively, you might choose to cast Infallible before you hit with Ice, which will boost your resistance-piercing capability.
If you don't like either of those options, you can also attack with another school altogether, such as Storm, Balance, Death, Myth, or Life. (Minotaur and Deadly Minotaur treasure cards are especially useful for bypassing Tower Shields.)
You receive your Ice Prism spell around level 12, after you have completed "No More Mr. Ice Guy". By exercising a tiny amount of patience, waiting just one more round, your 80% resisted Ice attack turns into a nice, boosted Fire attack.
If you have decent gear, a pet, and damage enhancements, you can probably one hit Jacques and continue your progression.
Unless that particular mob has a "cheat" where he instantly eliminates "Traps" you should not be having as much difficulty as your post suggests.
Use message boards such as these to look up strategies, gear and spell options/suggestions to defeat your enemy.
In my opinion, it is not KI that needs to consider revising the resistances given to Bosses, or certain mobs, but rather, your decisions on which cards are placed in your spell deck.
Always put prisms on the enemy BEFORE using traps. Otherwise your attack will hit the prism and disregard the traps. This rule doesn't apply to universal traps such as Feints or Hexes, so they can be used at any time.