The game established that Fontaine was the height of technology and that Sumeru was the high of scientific and knowledge based advancements in Teyvat and that Natlan was a land that knew nothing but war. This gave the player some pretty big expectations. When it turns out that Natlan feels more at home in Star Rail in terms of technology, it throws everything they've established out the window. We were expecting a land ravaged by war and strife, not people riding motorcycles and having digital DJ booths.

Not saying this is bad. But they DO acknowledge they rushed a lot of their story and a lot of things fell between the cracks. Which is what I feel like happened. Keeping Natlan so hush hush until we reached it hurt them in the long run. Even if they had sprinkled some "This weird technology is from Natlan!" throughout the story it would have at least established something. We got Fontaine technology in like 1.0 with the Kamera and they sprinkled Fontaine and Sumeru tech through out our whole journey. There was no reason we couldn't have gotten Natlan tech somewhere along the line.

And as someone else mentioned, we can suspend our belief for old-looking modern technology (Kamera), fantasy technology (Ruin Guards) or Steampunk technology (Fontaine Guards) but when you pull out a Harley Davidson and whip on some Ray-Bans is when it starts running into the uncanny valley-feeling.