No, you, as Sylvan elves, are in a good position in this regard; you have Wingael, and you usually have more mana than you need... But still, spending the first turn of archers or dragons on a level 1 unit – isn't that the very strategic advantage that makes demons worth respecting?

The most important strategic advantage is watching how demons drain the mana from a Barbarian and transfer it to a demon, considering that the Barbarian has upgraded magic resistance against darkness or chaos, and even better, both. Another strategic advantage is when a demon hero casts a combat spell on some Orcish unit, and a goblin shaman interrupts the spell on himself. Everything is relative, and if demons are useful against a mage, they won't do much to a Barbarian, except perhaps unleash their battle cries, but why would he need that when he can spend his turn on the ability: reinforcement, or just attack a unit?