Thank you for expressing that you have no fucking idea what balance is.
Talon's silence was not overpowered. The problem was that it was binary. The difference is that overpowered can be fixed by changing the numbers.
With Talon's Silence, you instantly jump beyond the average casting range of targeted spells, well before the missile of any skill shots could reach you. You then make it so that your target cannot use any spells or items--no hard CC, no defensive tools, no Exhaust, no Zhonya's--while you roll through your less-than-a-second burst rotation. Then, with the stealth from Talon's ultimate, you walk away from the fight whether or not you landed the kill.
It takes away the aspect of counter-play in a fight with Talon. He gets his entire rotation, it fully lands because you can't use anything to stop him, and then he either kills you or runs away (or in very rare cases, an ally uses CC or a pink ward so you can get him).
Katarina has no CC in her kit whatsoever, and the majority of her kit's damage is in her ultimate, which can be interrupted or avoided. Her Q-E-W rotation can't deal as much damage as Talon's E-W-Q unless Talon builds no damage at all. Her ultimate doesn't grant any defensive benefits, only the damage and Grievous Wounds.
Talon's kit needs redesigning, but I don't think Riot's going to rework him anytime Soon™
(you could also look into Evelynn's pre-rework issues for the same exact pattern)