Chaos is actually better than light for Necromancers, as it provides a lot of spells.
And if you focus 100% on being a warrior, light won't help you much. I've tested it; if you develop warfare, you don't get many spells, and the spells last for only 2-3 turns and don't help much. But, for example, darkness can be very useful in 3 turns, even with low spell power, and summoning is simply a great thing. You can place hordes of neutral creatures with minimal spell power, and the troops will be effective. So, light is a magic that I would personally develop last.