Magic in Heroes of Might and Magic V.

Darkness doesn't really suit an elf, unless in emergency situations.

First, provide arguments, and second, what is meant by an emergency situation? Personally, I know that with an enchanted arrow and several sworn enemies, you can cast several Berserk, Blind, Grief spells, etc., at once. In my opinion, that's quite effective.

No matter how long I play, I still can't effectively use summoning magic.

Summoning is not just about Phoenixes. In skilled hands, summoning can become a very dangerous weapon. The Fire Warriors perk at the start is a guarantee of further success and good help in the final battle, if the game hasn't dragged on too much. And there are other useful spells. For example, Celestial Shield, or Fire Traps – it's almost a cheat spell. Wall of Swords, with a certain landscape, can help trap some tanks, and can also cause some discomfort to cave lords, etc.