After reading the messages on this and other forums, I have the impression that Nival was forced to distance themselves from the plot of previous installments in order not to repeat the fate of the 4th part.

After all, most people expected Heroes 4 to be something like a new version of the 3rd, a kind of add-on. That is why many of the features and innovations of the 4th were met with hostility, including by me (especially the removal of the hero into the field; I even tried to play the 4th as if it were the 3rd).

By abandoning the old plot and creating a new world, Nival reserves the right to shape the laws by which the new Heroes will exist. And they are doing this—although they have already abandoned some of their inventions—perhaps for the best...

By the way, regarding opinions on the 5th.

My friend has written off the 5th part because "the hero was once again cast out into the field." For him, the 4th is nearly ideal, and it should have been improved, moving in that direction....
Oh, how I disagree with him....