Another one of my definite upgrades is the Sylvan Archers for the Elves.
I confirmed this in an Elf vs. Elf game, where I had the alternate units, and my opponent had all the old ones:
One turn of my Elves immediately took out all the enemy Elves because the initiative was better. (Even if the enemy Elves had gone first, there wouldn't have been such an effect.)
And regarding the bow, it's far from the most useful thing, IMHO. I prefer to increase the attack.
I agree. But until there are dragons, I prefer to make 50/50 Master Archers and Sylvan Archers. The alternate upgrade for Ents hasn't impressed me much yet. I still prefer to teleport the Ancient Ents closer to the enemy archers and have them root themselves right in front of them.
And the Light Unicorns. What the...? If you specialize in light magic, then maybe it's okay. But without the old, good magic resistance aura, Unicorns aren't Unicorns!