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Vis, regarding appearance, I was referring to your post about how external changes are significant changes for you))) this has nothing to do with the spirit of the game.
As for the story, the campaign for Gem was in The Shadow of Death, and before that, there was Armageddon's Blade and The Restoration of Erathia... did you play the Restoration of Erathia campaign?)) The intro even tells the story of how Catherine left Enroth and returned to Erathia... or is this not considered "mentions" and a connection between the parts?)
And I didn't understand anything about Jela and Tarnum)) Tarnum was in the Chronicles, which I didn't play, and I don't really want to (there are reasons for that)... and the 4th game starts with Jela and Kilgor fusing two super-swords, thus destroying the old world and forcing everyone to teleport to a new world... (it's absurd, of course, but there is a plot).
P.S. Yes, the world is different, but why mention heroes from other worlds (Kreg and Sandro) then?) In these parts, at least, there is a connection and a unified story.
Be strong. Believe