Man, the Champion of the first game must has been an absolute monster to be able to defeat Lethice's entire inner court and herself. I know it's not the same type of game, however I just can't help make the comparison.
I think that's the point, actually. No idea if this is intentional, maybe I'm just reading too much into things, but I figure the idea is that the Champion of Ingnam is supposed to be a lot stronger than the Champion of Frost, and this is the game's way of demonstrating that.
Mareth is, for all intents and purposes, a hellworld. Like, getting sent there is supposed to be an execution (for your soul), you're not meant to survive. In spite of this, the Champion of Ingnam gets tossed in with nothing but the clothes on their back, then proceeds to beat the shit out of an imp at level 1, start collecting demon skulls like they're trading cards, build a personal stronghold, and start recruiting allies from the wilderness.
They rip through every dungeon in Mareth
alone, and then proceed to knock Lethice off her throne in a 1 on 1 duel. SUPER intense trial by fire. CoC2's champion goes through a lot, but they're living in a place with actual civilization, and most of the demons they fight are either newborn imps or freshly turned I believe. Their origin ranges from no combat experience ever to a little bit of mercenary work in Belhar. Kasyrra literally lived through the fall of Mareth. She fought in a whole ass end-of-the-world war. And after becoming a demon, she's had who knows how long to ferment.
Also, I try not to compare stats from two different video games like this, but Lethice in CoC1 is level 25 if the page I'm looking at is correct. Kass in CoC2 is only level 20. The Champion of Ingnam can level infinitely, the Champion of Frost caps out at level 10. It's really hard not to draw some parallels there, considering Kasyrra wasn't strong enough to fight Lethice instead chose to just bail when the Champion of Ingnam showed up.
But hey, that's just a theory.