Sylvan vs. Necropolis

I didn't say anything about Light because your statement about it doesn't raise any questions; Light is usually a given for Elves, especially against Necromancers.
As for the difficulty, I play on Veteran with humans in the original Heroes 3.1 on random maps or in duels. There's no need to belittle opponents you don't know personally or haven't played with, and therefore don't know their abilities. Personally, I find this character development very reliant on a lucky combination of skills. If there's no mentor and good skills don't appear, the game will be lost, while the methods described here allow for any scenario.