Yvolka, Elementalist. Burst aoe high dps mage, but lacks utility and versatility (that was even discouraged from when she was young). Ie she is a OTP fire specialist and hence as shown earlier in the story a very key part to be succesful as Han/Loki mentioned.
Catio, Magic Scholar, so far we haven't seen him really output damage or anything but he seems to outshine Yvolka simply because hes a utility focused mage. A buffer, CC and utility spells like "inventory" and ability to manipulate concepts like propulsion.
The story is foreshadowing it likely but these 2 complement eachother very well. The party is like said 1 or 2 chapters ago build around Yvolka's fire with every member having fire resistance. Adding in a mage that can just efficiently refresh your main dps mage's mana as well as just add in buffs improving the frontline and damage of your mage AND lock enemies in place for your mage to just hit huge fire damage.
Come on author do you rlly have yo bully Yvolka like that. Han/Loki is basically going along with this to see the talents of Catio so he can optimize the strategy.
But damm Yvolka is done dirty. Han couldve just said thst what she lacks in utility she makes up with tons of ranged/aoe big damage and thry complement eachother