Enchantment is far more versatile than Construction just scrolling across the list of each shows the variation. Construction is very important yet if given the option of only one it's Enchantment.
Enchantment provides critical game spells such as:
Global Spells:
1) Earth Blood Deep Well
2) Arcane Nexus
3) Thetis Blessing (attacking water nations)
4) Gift of Health <Priceless)
5) DISPELL -- Taking out enemy globals!
Critical Battlefield Buffs:
1) Strength of Giants
2) Flaming Arrows
3) Anti-Magic (entire army!)
4) Haste
5) Arrow Fend (major)
6) Mass Flight (major during storming castles)
7) Mass Regeneration
8) Long List of battlefield spells for resistances
9) Storm Warriors
Great Battlefield Spells:
1) Unraveling (magical units go Snap-Crackle-POP)
2) Raise Dead or Skeletons
3) Foul Vapors
4) Heat from Hell or Grip of Winter
5) Rigor Mortis
6) Mists of Deception (recently identified as being too powerful)
7) Demon Cleansing (double damage on demons)
8) Friendly Currents (underwater spell)
Important Teleporting Spells:
1) Cloud Trapeze
2) Ritual of Returning
3) Faery Trod
Good List of Summoning Spells:
1) Revive King / Create Revenant
2) Claymen (underwater optional)
3) Pale Riders (underwater optional)
4) Enliven Statues (underwater optional)
5) Reanimate Archers (one of the very few archer summonings)
6) Carrion Reanimation (major)
7) Lichcraft
Good Offensive and Defensive Spells:
1) Army of the Dead
2) Seeking Arrow
3) Most of the DOMES are here
Good Buffs helping SC's types to actually stay alive:
1) Breath of Winter
2) Resist Magic
3) Personal Regeneration
4) Astral Shield
5) Flight
Second Chance Spells:
1) Ritual of Rebirth
2) Twiceborn