Why is kassadin overly forgiving?

It makes no sense to me.

He can go electrocute resolve. Dish out a fuck ton of damage while taking very little in a trade. He can also go the fleet build for infinite sustain. There's so many routes for him to take to at the very least have an easy laning phase. But considering he hard counters half of mid lane (I kid you not half of his "counters" are ad top laners) Most of the time he doesnt need a surviving laning phase, he just ends up dominating. A champion with one of the strongest 16s in the GAME, should have a dogshit early. Or at the very least be easy to punish. But he isn't. His mana costs, are super easy to manage. Everything about him screams "im ahri but as a hyper carry" and its insane to me that riot cant seem to draw the line between surviving lane to scale, and just dominating with free earlies into accelerated scaling