Why do resets even exist?

A typical mage can blast off ~50% of an enemy team's collective health with a solid QWER combo because AOE. Many of them can also poke an enemy team down low enough to take out ~50% of the enemy team's collective health if played well, and pretty much every mage can lock-down at least 20% of the enemy team with hard CC to hit the equivalent of a 50% contribution.

Any marksman can take out ~50% of an enemy team's collective health through auto-attacking long enough, mostly just requiring good positioning on their part.

A typical assassin? Is hard-capped at 20% of the enemy team's collective HP is all they have is 1 rotation of a QWER burst. Enter resets, which allows assassins to take out ~50% of an enemy team's collective health if they're played well. Some assassins also rely on mild AoE power and amazing AA steroids to get a bit of mage and marksman power.

That's the basic reason for re-sets, keeping melee burst as not-completly-worthless in team fight situations

(It's also worth noting most supports and tanks can incapacitate ~100% of a team long enough for half of it to die under the same kind of optimal situations a marksman or mage will take out ~50% of the enemy team's HP).

Anyways - Kat clearly breaks from that patten by having a ton of AoE power.

It's worth noting her QWER damage isn't that impressive compared to mages like Lux, Ziggs, and Xerath that can do the same damage from much greater range though. It's also worth noting Kat can't activate Zhonya's mid-combo like other AP carries who have the strategy of physically throwing their ~squishy selves into the middle of an enemy team ( ).

Also - Kat is only one of ~10 champions in the game with no form of CC at all. No mini knockback, no minor slow, nothing. Her only contribution is AoE damage, and her QWER is actually taxed pretty heavily to set up a reliance on resets to match what other mages can do. Fiddlestick's QWER combo actually does nearly twice the damage as Kat's, and he actually has hard CC, range, and can Zhonya's mid-combo. So while Kat's resets are a little unconverntional given her strentghts, she also pays heavily for them with her kit's power budget.