Did you forget, or maybe I missed it somewhere, that Wing's ability isn't just strong, but also a very important starting skill – Attack, which the other heroes of the Sylvan faction lack. When Wing isn't banned and appears in the tavern as the 2nd hero, along with Ossir... well, it's a dream come true. You forgot to mention a hero who is worth considering, especially in the ultimate/late game (although these stages of the game aren't that popular) – that's Anwen. Anwen's bows deal almost as much damage to spellcasters as Ossir's. Her starting skill isn't particularly outstanding, but she's still a hero for longer games, and as you know, the "Defense" stat (as well as "Knowledge") is the main stat for Sylvan heroes, so the Defense skill will significantly reduce the damage taken by Sylvan units; I even tested this and was slightly shocked.

Overall, we can conclude that the Sylvan faction is more suited for duels than for battles on maps.

What is this nonsense? In your hands, this race might indeed be only for duels.