In the final stages, it's just a nice feature, good for a single, decisive strike, but nothing more.

What about immunity to Darkness and targeted spells?

What prevents you from still deploying only Stalkers? Or, in general, stop scrimping and fighting with a normal, large army?

I could defeat a significant number of Titans without any losses, simply by having only Stalkers and Mistresses (and, of course, a hero) on the battlefield, thanks to the Invisibility ability. But if I deployed everyone, I would get my butt kicked.

Witches only shoot at half the battlefield, which means they need two shots for full damage. Well, for full damage in one hit, our Mistresses also need at least two turns, the only difference being that anything can happen to them along the way, up to an encounter with a Devil.

In general, this unit, judging by its speed, is not designed for attack at all. They can calmly go invisible and wait for particularly agile enemies, and no one prevents them from casting spells while invisible.

And now imagine - they go invisible, and the attacks start hitting the Riders.

By that time, the Riders will either run to the other half of the battlefield (may they rest in peace) or get beaten by fast-attacking troops like Nightmares or Paladins. Everyone tries to eliminate them immediately; the Witches have nothing to do with it.

If I have a choice - to lose a couple of Hunters when breaking through, or to lose an extra five minutes painstakingly arranging, moving, and calculating all possible Witch movement paths, I will choose the first option.

Okay, if it's a couple, but what if it's a couple of dozen?