"Necropolis" - changes to creatures of levels 6-7.

He doesn't need to raise them. Zombies have good growth, which practically doubles with the presence of any secondary castle. And they hardly die in battles.

Well, it's clear that we're not evaluating a single unit (otherwise, we could conclude that assassins are the best at their level), but rather within the framework of Power growth per level. The Necropolis has the ability to double growth from any other castle at any level; in this regard, zombies don't become relatively better than other Necropolis units.

You have a different concept, the concept of tanks. The original zombies have the concept of cannon fodder. I'm not going to judge which is better; they are simply fundamentally different, both of which are viable.

Indeed. The concept of cannon fodder is precisely what leads to zombie hordes, which is what we're talking about. And here's the problem: mostly slow units are used as cannon fodder.

Added 23 minutes later

After all, troops always act together, and zombies work well with other units, being the thickest cannon fodder in the Necropolis, holding out until the very end in any battle.

As far as thickness goes, as I recall, ghosts are just as good, considering their incorporeality. They just take more damage from magic, which ignores incorporeality. The damage is roughly at the same level, and their speed and initiative are significantly higher. In general, ghosts are among the best at their tier (after elves and, possibly, bears), but they don't have a hero specializing in them, and they are often used as single units (the best for this role), being actively used as expendable units.