Chaos magic. Is it necessary?

Yes, BUT the Elf has low magic skills (I'm not considering cases where the hero finds the Cloak of Sar-Iss), so it only makes sense with an enchanted ballista. Or, if you're lucky with your sworn enemies, you can have the hero attack multiple targets. However, if you're unlucky with enemies and machines, then chaos and summoning definitely don't work; you need to go with light magic...

But new Druids appeared in 3.0 with a skill that increases the hero's magic.
I haven't played Elves much, but recently I played against an Orc on ubi, and my magic skill was 35 at only level 20, and I think Shock of Earth dealt 2160 damage. Although the Orc figured out the trick with chaos and managed to find items that provide resistance to chaos... With a pendant of mastery (i.e., 4 sworn enemies), the hero only needed to attack twice; it wasn't necessary to attack more. The enemy didn't even have time to kill all the Druids, so the magic skill wouldn't decrease... and even if he had, the outcome was already clear.
So, in the new game, I think chaos + defense is a viable option.