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On Normal difficulty, Angels are used in 9 out of 10 cases on the 2nd week, if the goal is to reach the Capitol on the 1st day of the 2nd week. Yes, you have to survive for 2 weeks by gathering resources, but even with un-upgraded Angels, you can quickly catch up. But Necromancers also don't develop very quickly in the first week without Dreadlords!
The discussions about levels 2-6 are unclear. In the end, there will always be a battle between Skeletons vs. Archangels. By the end of the 2nd month, the Necromancers will have around 3,000 skeletons against about 15 Archangels.
Most likely, in an open field, the skeletons will reach and chop everyone to pieces, but in a castle, there are possible scenarios... (and skeletons in a castle are also not ideal for them; they need space).
Based on my own dueling experience, everything depends on the nuances, but Humans vs. Necromancers is always interesting! Will the Humans have the ability to hire Angels, how many Conservatories do they have, how many Utopias did they take, what magic or artifacts do they have? Everything can be decided by a small ring +1 to life - and if there are 3,000 skeletons, that's already 3,000 hit points!
Although, purely IMHO, gathering skeletons is a rather boring activity...