Or "Order has the coolest magic." Or "let's say you have the Ring of Great Negation"... Ugh, I got distracted.
So, here's the thing.
There are rush maps. On them, rush factions are the best. Barbarians. Then Humans, Chaos, and Nature (because of access to the Archer).
There are development maps. There are monster maps. There are "hero" maps. On some maps, there's no hut for scouting. On those, factions without access to a fast unit have a harder time. On some, there is. On those, it doesn't matter much. On some maps, there are fixed major resources. You can develop based on them. On some, the major resources are random, and on some, there aren't any at all. And you can go on like this forever...
In general, there is no weakest faction in Heroes 4.
There are just different maps, on which some factions are more convenient and others are less convenient.
And there's also Equilibris, which balanced the imbalance of monsters and spells of different factions to a quite decent and acceptable level.
In general, play with strong opponents online. And you will be happy. ;)

