Tactics for playing as the Sylvan faction.

Moreover, these elves aren't that proactive, and the hero is generally weak.

As far as I know, they have the highest average initiative, perhaps only matched by the Warlock. With Wing, this parameter increases even further. Their hero is indeed usually weaker than the mages, but this applies specifically to the hero's turn, and there are also passive abilities. And in terms of these, the elf outperforms the mage (unless the mage's development comes at the expense of the hero's strength).

And they also have archmages, who are also warlocks, and they will be better than druids.

In the late game, the role of magic decreases, and the role of ranged units increases. And the ranged units of the elves will be better (especially if you take the Sylvan faction, their initiative is 11 against 10 for the mages), and druids can be used for "channeling," which will strengthen not only the hero's chaos spells but also some light spells (like resurrection, divine vengeance).