I assume english isn't your primary language(or even secondary) since you completely missed the point of my comment.
Karthus' ult, Tahm Kench's ult, Rek'Sai's ult etc. are channels. Silences, stuns, fears, knock-abouts, charms, taunts will stop them and in case of Tahm and Rek also taking damage does it.
There is no practical reason for Ezreal and Lux's ults to not be channels.
They should be used at long range and casting them in melee range should be punishable. It's not.
On the other hand there is Ezreal's Arcane Shift.
If we break it down, this is what happens visually:
Ezreal creates a portal in front of himself, then proceeds to jump into it and get teleported. The time he begins creating a portal and jumping into it is the "cast time".
Except if somebody knocks him out of the jump and away from the portal, why should he still get through it?
Thematically, it's plain stupid.
Gameplay-wise, it's plain stupid too.