Royeeeeeeeeeeeeeeeeeeeet What's kassadin's role?

I've just watched a fully spoon fed kassadin get his butt handed to him by a jinx with an The kid was fed and thought jinx was going to be free gold, he did his thing, flashed, unleashed his full arsenal q w e whatever, and brought her down to 60% hp, but jinx just stood there and killed him within 4 autos.

What's kassadin's purpose now? he cant no longer burst down anyone, hes not tanky, he doesnt have his silence, nor does he have his teamfight potential with his aoe. Even LB can do more dmg then kass.