Necropolis and Demon.

What is being demonstrated in this case: the player's skills, their gaming experience, etc.?

Imagine, yes, the player's skill is being tested. I played against another Necromancer (there was this guy who vehemently insisted that he would crush me with Necromancers, but unfortunately, it turned out to be the exact opposite). Not only did he assemble a truly terrible army for a Necromancer, but he also lasted only a turn and a half under the pressure of the summons. Doesn't this speak to the player's skill, or rather, "lack of skill"?

Just make a map where you can level up to the maximum right away...

This map has level 35, which is the maximum. I don't understand what other maximum you need.

And what's the point of the "Call of Urgash"?

Probably to double the army size in the very first turn? Think about how quickly I would have been defeated if I had to wait another turn for reinforcements to arrive? And don't try to use "fast gating" as an argument. With "fast gating," the summons don't appear faster; it just reduces the initiative cost for gating by half, meaning the unit that used gating is pushed back not by 0.5 on the ATB scale, but by 0.25.
And why would I need Light without Divine Retribution, Mass Divine Power, and Smite? It was completely useless in this match, like "why would you need a balalaika on a pig."