If we're going to be looking at Assassins....

Then we need to talk about this guy.

Firstly, he's problematic. He has always been problematic, which is an impressive feat for a champion with several ability reworks that's been around since the beta. Whether not-weak, which means he's unstoppable, or weak, which means he scarcely sees the light of day, Kassadin's inherent broken issues make him a nightmare from a balance perspective, though the reason why is interesting.

To put it into shorter terms: His primary thematic (Anti-caster dude who fucks up casters by disrupting their ability to retaliate and stabbing the shit out of them) and defining gameplay attribute (nearly unrivaled in-combat mobility) conflict in the worst way possible with his usual gameplay pattern (dump a freight-train's worth of burst into a carry's face after blinking in, then blink out.)

Kassadin's original (talking waaay back) design was "melee carry." If you looked at his kit through that lense, it makes sense:

Passive: Take less Magic damage (there was no such thing as non-Magic abilities then), get attack speed for taking magic damage (nuking him helps him.) Q: Silence (stops caster from retaliating properly, lets him stab them) W: Stab people get mana, active armor pent E: Same as it is now, cast spells=Kassadin profits. R: Sticky as hell, mana-gated, needs to auto to maintain.

So what happened? Well, his spells had huge bases and ratios, because that's how things were then. So people built him full AP and he one-shot people during a silence after blinking in. Oops.

To make Kassadin healthy, his kit needs to be moved in the direction of auto-attack focused, with his abilities serving as mechanisms to enable him to do that without simply dying. The main way he plays now (insta-burst bullshit) has been the only approach that Riot has really acknowledged for him, and it doesn't work.

There's plenty of room to work with this idea, and with this thematic and defining characteristic, and I'd love to see it happen. This isn't just about Kassadin's balance state, which has historically been chaotic, it's about how his thematic elements fail to mesh with his gameplay patterns, and it makes him feel a lot less satisfying than he should.