Alright before we get into this, I will say this:
This post is an opinion. Not fact.
I'm open to discussion, just don't be an arse.
Let's look at what an assassin is meant to be.
-An in-and-out playstyle champion meant to eliminate one target and then get out of the fight.
So, a good burst champion that is able to get out of fights quickly. Sounds pretty good, right?
How about LeBlanc?
- Insane burst damage
- Able to get in and out of fights quickly
- Able to deceive her opponents with her passive
No. Not LeBlanc. She does too much damage too quickly while also able to immediately leave the fight at any point if she wants to.
Zed? Again, too safe, too much damage
Fizz? Too safe, look at his E.
Talon? What's with these champions and their E ability? WAY too safe.
But how about Katarina?
- Good burst damage
- A way to get in and out of the fight quickly (with her E)
- And a really fast playstyle.
I think Katarina is the best designed assassin because of her passive. When people complain about assassins, they complain about them being too safe while also being able to just eliminate one or two people from the team at the same time. But with Katarina, you don't have that. If you can't do your job, you're not getting out without intervention.
Think of this:
A 4/0/1 at 20 minutes Katarina goes to help her team contest a dragon. She uses Q, E, and R to deal a ton of damage and kill someone. She is now allowed to leave the fight if she wants to or keep fighting. She decides to keep fighting. Since she doesn't have her R or Electrocute anymore, she is now unable to deal as much burst damage. She uses Q, E, and W to deal a good bit of damage. She's still able to leave the fight because her W reset her passive, but what if the enemy team played around her properly? They would zone her away from her W so she's unable to get it, and then she's left without an E, and is an easy target to kill, unless she flashes away or her team does their job and protects her.
See what I'm getting at? She's designed to be EXACTLY what an assassin is meant to be - a lot of damage with access to a quick escape option, however that option isn't always available, therefore she can be played around and countered properly. If she can't do her job and nuke someone down, then she's unable to get out and dies. This should be exactly what assassins should be modeled after.
At the moment, though, Katarina's damage is just a bit too high so some light tweaking to her ultimate scaling and passive scaling, along with a small base damage increase should bring her back down to earth without gutting her if she's behind.
"But what about high level play!?!?!?!?!?!/1/?"
In high level play, the same thing applies. Katarina can be played around and counterplayed, so therefore she has to be good enough to do her job and get out of the fight before the enemy team can kill her.
TL;DR: Katarina's the best designed Assassin simply because of her passive and her E interactions with her daggers. It allows her to escape if she does her job correctly, otherwise she is punished and subsequently killed.
As I said before, I'm open to discussion.