On the 5th level, the game is indeed very difficult, but not because of the combat system, but because of the 1.5x increase in enemy armies – you can't defend against all of them. Just like in Heroes 3, there were Pyrrhic victories when only a few level 1 units remained from a huge army + victory!
As for the game being geared towards the masses, Ment answered this question himself by supporting Zubr, even though he didn't fully understand it. Not amateurs, not professionals, but fans – those who are fanatically devoted to their faith, their idea, and don't think for themselves. Because the more limited a person is, the more they try to copy others, those who they consider smarter – and that's how a crowd grows. Heroes 4 is more complex than Heroes 3; you have to think more. But real life is even more complex; you can't replay it or change it like a game – you have to study the existing rules and live by them – or not live at all.