So if your attack with this guy causes a Narcomoeba to be milled, they get it. If it gets dredged on your turn, they get it. But if it gets dredged on their turn then you get a zombie and they lose the 'moeba. It might be a decent defense against some other parts of the dredge engine, but not 'moeba.
I wouldn't want my second attack (after picking up a few zombies on the first swing) to mill them into 4x Narco and 4x Bridge from Below. Sure they can't really dread return anything, but they can get 4:1 ratio in Zombies created per Cabal Therapy.
The best play with this guy would be to swing with the tokens you get, but hold the guy himself back. It becomes very difficult for them to get anything into pay at that point.
Leyline is still likely to be better given the speed of Vintage decks, though this guy does dodge Nature's Claim.
His replacement effect applies to the other zombie tokens you get from him (they're Zombies) too, so I'm not sure how not attacking with him nets you anything?
And yes, I think Leyline is miles better.

is only marginally easier to cast than

(dependent somewhat on deck choice), given how often you'll need Black Lotus to cast it in time to be meaningful, and given that most of the time you'll mull into a Leyline you get to start with for free.
I think a 3/2 for

would have been slightly more competitive, and also more sensible. I don't get all the blue zombies in this set at all. Apparently the justification is "mad scientists and frankenstein's monster!!!"