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actually, all 4 Castles from the first game were carried over to the second, plus two more were added (Undead and Magic), which blended perfectly into the world, and let's not forget the Might and Magic lore.
In the third game, there were even more changes (+2 Castles: Inferno and Swamp, although Stronghold can also be considered), but they mainly complemented the world that already existed...
They also changed the hero window (it's a small change, but a good and logical one), moved some units, added new ones, although this mainly affected Dungeon and Barbarians, and one level 1 unit was added to each Castle.
At the same time, the entire story, some heroes, etc., were preserved.
As for the fourth game, yes, there are even more changes here, from changes to the battle system to the relocation of creatures. Although Dungeon has become similar to what it was in the second game, so it's not critical for it, as it is for Humans, Magic, and maybe Barbarians, since they changed in every part. But they merged Undead and Demons, which is very noticeable, although if you build along one branch, it's not that noticeable. It's more difficult for Elves, since half of their units are new.
The overall style hasn't changed much compared to the fifth game. Everyone lives where they lived (in terms of location), maybe except for Dungeon, but it's a nomadic Castle, and the story remains consistent.
P.S. I've already written about the Spirit, but you only focus on the appearance and ignore everything else, not even commenting on it.