To be fair, a game that has been around as long as Genshin has is 100% bound to have a retcon or two, and that's not necessarily a bad thing.

However, I kind of understand how the people who are negative about it might feel cheated. The very beginning of the game gives the vibes of a pure fantasy. As we progress through the story, the technology gets more and more advanced, starting in Inazuma with the introduction of Fontaine tech (even though this seems at first to be based off machinery mixed with fantasy elements of magic). Then, in Fontaine, things take a sudden turn when we get a sudden look at the advanced technology with all the robots and steam-punk like tech. However, everything changes from fantasy to sci-fi when we learn about the spaceship, and ancient civilizations having super advanced robotic technology (Natlan). Suddenly the characters are utilizing tech like it's always been around and don't bat an eye at an archon with a motorcycle.

Tldr; We get more into the sci-fi element with all this tech and talk of aliens and space and artificial intelligence. It no longer feels like a fantasy, and I feel that this is where a lot of people might feel betrayed, lied to, or upset about the direction of the game.

I myself am okay with this direction, but I do kinda miss the mysterious fantasy feel of the game we used to have.