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Hello Kiko!
The answer is YES and NO at the same time.
With the current changes, we lowered the power of Might heroes and increased the power of Magic heroes.
In Heroes 5.5, Might heroes are more like fighters + supporters of the army.
Magic heroes work more on their own because they cast magic more often (expert sorcery is 36%), and their magic power can be further amplified (Occultism tree).
What you are talking about in the old Heroes 3 is an imbalance. Attack and Defense gave too much power to the heroes, so in just 10 levels, they could easily dominate the map. The same can happen in Heroes 5.5; you only need to be a much higher level.
When talking about the army numbers, this has nothing to do with the heroes.
The advanced ARMG made it possible to create larger maps with more castles and gradually increasing monster difficulty, which was totally lacking in Tribes of the East.
Due to now having more castles and stronger monsters, everything else happens naturally.
For example, having a big map means more castles and time to play before finding your opponent.
More time and castles mean the possibility to develop more of them and get more creatures to overrun your enemy or fight stronger map creatures.
The need for more creatures and development means you will need to find/gather/mine more resources.
The way the game develops is now more similar to Starcraft. It is just as much about fighting as it is about economics.