The game balance in version 4 is almost non-existent. Some units and heroes become so overpowered that it's simply a bug. For example, a Druid from the Nature Castle can single-handedly destroy a Quicksand Castle. The financial aspect is also flawed: the Order Castle is incredibly rich, while the Chaos Castle is expensive and unprofitable.

Unfounded remarks. Those who know how to play won't have such complaints about the balance. In the original Heroes 4, Nature was by no means the strongest race. It was simply strong among equals. A small example of the weakness of "overpowered Druids": in the regular Heroes games, Order magic works regardless of the line of sight, meaning Druids cannot hide behind summoned creatures. They can be hypnotized and forced to kill themselves with their own hands by attacking Phoenixes, for example.
However, the Order Castle is not particularly wealthy. No one levels up Lords in battles; experience is valuable for combat heroes. At most, they send Lords to collect all the free power-ups and try to raise their nobility to expert level (which rarely happens).
Chaos, on the other hand, has Thieves to maintain balance; you can gather far more resources than a slow, un-leveled Lord could.
In Equilibrium, it's difficult to argue that one race has an advantage over another... the balance is almost perfect. The problem is that a Tactician and a Runner have become essential for absolutely any army... but this is not a racial imbalance; it's an imbalance in the applicability of heroes. And you can easily come to terms with that. :)
Conclusion: play as different races, play against real people. There is no bad balance; there is only a poor skill level. :)