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

I disagree; on a large/huge/rich map, Haven is undoubtedly the strongest faction.

Not quite... because with a large army, the damage dealt is also significant, so Dark Magic (especially Implosion) can be very helpful here. Then, half of the human army can be killed by... for example, Paladins. And the "Purify" spell won't always help.