Just look at the stats: 9/7, haste, lifelink, and indestructible
If you're starting without any Zombies, it takes a very long time before you start amassing a large battlefield of Zombie tokens, and at that point, you likely could have built enough of an army of regular creatures
Im, generally speaking, a big fan of cards that answer more than one players problems in an asymmetrical way, but I am wary of how this ends up, in practice, as power creep
Its the activated ability that really makes this card shine
Luckily while you wait for this to happen, you can draw cards and lose life for exiling cards from your graveyard and/or battlefield, giving Ketramose, the New Dawn some early game relevance before it becomes a game-ender
The defending player can assign blockers normally as long as they are black and/or artifact creatures