Necropolis or Castle (Which one is stronger?)

These spells are effective when the corresponding artifact is present.

When I mentioned "strength," I was referring to the strength of the units. This is a more objective indicator. Of course, it also depends on the hero, the conditions, etc., but all other things being equal, these two Castles have some of the strongest unit sets.

It's difficult for me to agree or disagree with you, as it's hard to say definitively. The fact is that I calculated the average attack and defense, speed, and health of creatures from all factions, taking one unit of each level (unimproved) and it turned out that the Castle was in the top three in terms of attack and defense; the Citadel has the highest attack, but at the same time, the Citadel has the lowest defense, the Fortress has the highest defense, and the Conflux has the highest speed. In terms of the sum of attack and defense, the Castle came first, and the Dungeon came third. I immediately say that this analysis is clearly illogical and not entirely accurate; I just wanted to have some idea of the factions and their characteristics. Therefore, I ask you not to criticize these calculations, as I myself agree that they are not objective, and many will want to dispute them. However, I understood and confirmed that the Fortress has excellent defense but low health (although it was clear even before), the Citadel has the strongest attack, etc.
And yet, who is the best is a pointless debate in which it is almost impossible to find an answer; everyone decides for themselves.