The 5th installment has no connection to the other parts.

I disagree. There should be a connection because there are some things that were taken from the third game. For example, Sandro's cloak. Or read about the necromancer Lucretia, who was seduced according to the description. This means that Sandro as a lich and a character already existed. Therefore, Ashan is another name for Enroth, and it's a new kingdom. And the units remained the same. That is, the events in the 5th game take place after the great war, which devastated Enroth, and a new kingdom, Ashan, arose. And then there was a demon uprising, the separation of the necromancers, and so on. That is, the land is the same, but the names are different.