The essence of the tactics when playing as the Dark Elves.

I disagree with this example. I played against Former Friends and Kaspar as well. I cleared the entire center on the 2nd week without any problems.

Kaspar is already in the center on the 4th day, defending his artillery and then running towards yours. And if you plan to clear the center on the 2nd week, you won't even be allowed into it. Moreover, it's very difficult to chase after artifacts and experience while simultaneously running away from the enemy. And when Letos and Kaspar clash (130-150 skeleton archers, a lot of meat, and a tent with 150-160 resurrection/damage), the former is practically doomed. And considering the specifics of the center, raising 8-9 vampires by day is also not that difficult. And if you ban Kaspar, you should also ban Letos, and that's a completely different game.

With Crystal, there's some kind of bug in the AI's behavior. This spell seems to be specifically designed for Necromancers. If there is no enemy on the battlefield (Hunters are in invisibility), the Idiot (you can't call it Intelligence) considers Crystal guilty of all mortal sins and attacks it. This is easy to exploit: place Crystal next to a stack that moves later (and in the case of large creatures, even next to two), and the stack that moves earlier will blow itself up, along with its colleagues. Moreover, Black Dragons take full damage, despite the magical type of damage from Crystal.
And Crystal's damage is pretty good. And Earth Lord also affects it...

Crystal is a great thing. But setting up the Guild and learning takes a lot of time, plus you also need to get Summon on the first upgrades and level it up. And there are not always enough mines. Kaspar would also like to have Fire Arrows, but you can get them on the 8th day in no more than one out of five cases. And with normal Summon leveling, the Warlock will have a similar situation.