The problem with Warcraft humans is that the majority of the kingdoms aren’t expanded upon. Humans have multiple different empires with the only ones that bleed together being Stormwind, Lordaeron, Alterac, and Stromgarde.
The issue with these four is that they are old. What I mean by this is that Lordaeron, Alterac, and Stromgarde have been prevalent since the old Warcraft games; outside of their gimmicks, they end up being pretty similar to Stormwind in terms of culture and lore because they mostly serve the role of being a “human kingdom”.
Lordaeron: Forsaken
Alterac: Syndicate
Stromgarde: Literally just the color red
This kinda makes them all look very similar to eachother since their story relevance died before Blizzard cared about elaborating on the human kingdoms beyond the fact that they are kingdoms ruled by humans. Not to say they don’t have defining features, but compare any of these to the other three kingdoms: Kul Tiras, Gilneas, and Dalaran.
These three are actually pretty interesting and they have some unique aesthetics. Additionally, you can see how Kul Tiras was developed past the previous problem, as they started out as the “human kingdom with boats and the color green” and later became the second most developed human settlement on Azeroth. The issue with these kingdoms is the last two, Kul Tiras was actually good on this point.
Gilneas was basically dropped by Blizzard post starting zone, and at this point the Gilneans gimmick is moreso that they are dog people 85% of the time instead of their British inspiration.
Dalaran has become such a neutral ground that its more of a hybrid between Hogwarts and the Avengers rather than a human kingdom. If you didn’t know that it originally was one of the human kingdoms before seeing it in-game, you likely wouldn’t even realize that it was one.
tl;dr: most human kingdoms are either irrelevant to the story blizz wants to tell, meaning no story development to differentiate them from SW, or they are so consumed by their gimmick that it supersedes the “human kingdom” part of their lore.