One-on-one battles are actually more challenging, as the AI opponents start eliminating each other, and their armies become weaker...
With Kifara, mines are usually taken in the second week, which is quite easy.
With Vaishan, you can even get crystals in the first week, and sulfur is built in the castle.
One of Kifara's main advantages is the Ice Golem! When used wisely, it's a very powerful unit! Vaishan, on the other hand, has almost uncontrollable mines!
Please provide the name of a map against Necropolis; I'll play it and share my observations.

Added after 9 minutes
And 250 per day is quite good, in my opinion, considering that the Tower's army is the most expensive.