In your opinion, which faction is the strongest in Heroes 5? Let's discuss the advantages and disadvantages of each faction.

but the artifact for increasing skills is just a one-time trinket for them!!!! the same goes for the light elves, but they weren't in the campaign (why, by the way)

It's unlikely that the artifact for light elves is just a one-time trinket. For example, if you play as Anwen, it's a game-changer, and it's also useful for other heroes. Double damage (and if you get lucky and play as Anwen, it's even more...) will be helpful to anyone!