With Kifara, mines are usually acquired in the second week, which is quite easy...
With Vaishan, you can even get crystals in the first week; 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 Tribes of the East army is the most expensive.