Now, about the balance. Inferno is one of the weakest Castles. There is Deleб, but that is the hero's strength, not the Castle's. If you play without it (and often it is banned in tournaments), you get an incredibly difficult start right from the first days and an inability to fight on equal terms in the final stages, from weeks 4-7.
Next, about the Dwarves. They are strong in defense, when defending the Castle. And then what? They are very vulnerable to rushing. The option of sitting in the Castle is a utopia, because your territory will be taken over, and the rush will turn into a regular attack, but with an overwhelming advantage in forces, and then even a Tower won't help. Again, a very difficult start, especially without the Rune of Energy, while any archers/casters become a death sentence for the army. The race is very focused on defense; you need to get magic of light with good spells, etc. Although the Armageddon build is also possible, but it is unpleasant because it depends on a lucky spell and a Rune of Resistance. Yes, there is a cheaper construction of economic buildings, but the cost of building creatures is very high, mainly due to the large demand for crystals and gems (thank you, patch 2.1, because in 2.0 it was possible to build anything). Dragons? You still have to survive until then, and their parameters are quite compensated by the "elemental" property; you can't cast "resurrection" on them, although you can't cast "enslave" either, but it depends on who you are playing against.
Yes, there are races that are effective in rushing, and there are those that will dominate in a long game. But that doesn't mean that the former will always win against the latter (which, in the absence of balance, would be a 100% probability). So, in general, the balance in Heroes is excellent and is improving from patch to patch.
P.S. Although most people tend to believe that the Shadow League is superior to the others