Does Zed even need the AD scaling on his ult?

For someone with one of the arguably safest assassin kits, why does his ult have an AD% scaling at all? The whole point is he goes in and Marks you for death. The whole point is he has to do damage for the Mark trigger to actually do damage. So why does it need an AD% scaling at all that makes it almost entirely irrelevant in some cases? It's different from pretty much every other massive burst assassin ult.

Talon/Rengar/Kha'zix/Akai/Nocturne have to go in. Kat/Xerath/Malzahar have to stand still uninterrupted without Zhonya's. Yasuo has to go in and only if they've been knocked up first. Riven's ult does almost nothing by itself because it scales with % missing health meaning she has to actually work for it. So on and so forth.

So why does someone with an ult that safe and an inherent passive that handles said missing health incredibly powerfully even need an AD% scaling at all in the first place? Focus all the damage from the ult on the copy-nuke. If he doesn't actually work for it, no need to reward him.