The most UNPOPULAR faction in Heroes 5.

Elves... What a mediocre race - besides the Hunters, there isn't a single decent unit... The heroes' magic is also terrible, as are their abilities...

Dryads are one of the best level 1 units (initiative, speed, attack on multiple targets, retaliation).
Dancers - the upgrade makes them extremely dangerous (the damage may not be great, but their speed, initiative, and attack on all nearby enemies are).
Hunters - everyone already knows that.
Druids - both archers and spellcasters, and they are equally good at both casting spells and shooting.
Unicorns - magic resistance aura, blinding, speed, initiative - useful both in defense and attack.
Ents - the damage and initiative are small... but they move well, and I won't even talk about their defense (especially when they are entrenched... they also constantly retaliate). They can be used both in defense (to protect archers and druids) and in attack (to entangle or block anyone).
Emerald Dragons - one of the strongest level 7 units, and probably the most useful (initiative 14... speed 9... breath attack...), as they move among the first and fly very far.
Honestly, I don't know who has a better army quality than Sylvan...
Here are the racial abilities... not the best... but with skillful use, they can greatly ease the game. I also have complaints about the hero's stats... too much "knowledge"... although with a certain hero build (Expert in Chaos Magic, Rain of Arrows, Enchanted Arrow, and 3 or even 4 units of Cursed Enemy...), it might not even be enough. Light Magic will be more useful... and there is more than enough for mass spells.
Skill drops... it's a pity that Attack is rarely given... the other useful skills drop often.

If the hero is Wingael (his ability is even a bit of a cheat), then the Dungeon has a sharply reduced chance of winning (against Wingael, almost everyone has a hard time), as this guy's troops will crush the Warlock's army even before his first turn, and if they also get lucky and strike... the morale will also drop.
Ossir - starts very aggressively (he has a dozen archers from the very beginning).
Anwen - if she develops, the Cursed Enemies won't survive.
Gilraen - by the final battle, he can gather an army of dancers, who under his command turn into butchers.

So, don't criticize Sylvan if you can't play them well.