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To me, it seems more like a mix of Heroes 3 and Heroes 5. There's almost nothing from Heroes 4 in it.
And for me, it's easier than Heroes 3 and 5.
As for Heroes 4, I don't even consider it a Heroes game, especially that part where units move without heroes, and heroes move without units – it reminds me more of some Diablo game, which is nonsense.
So, I don't understand where the connection to Heroes 4 is, although this is just my personal opinion.