Which units would you like to replace/add?

But they are not very effective. And they are not particularly impressive in terms of appearance. Although, in principle, it's a matter of taste. But I would remove them.

One of the strongest strategies is a rush with Orson and zombies. Week 3-4, quantity ~200 (+-50). This eliminates quite a lot and is very difficult to counter. So, just because you don't know how to "prepare" them doesn't mean they are "useless".