It could be argued that Chinese has a lot more characters to learn if you're including the Nanori (Readings used in Names) for 生.
If you take a language like English, it's still arguable that you'd need 12 years worth of schooling to do an advanced test.
Kanji Kentei seems to ask esoteric things at level 2. So it's a test of fluency of not only the Kanji but the language.
How would an English learner fare with Shakespeare or reading a book like Finnegans Wake?
I don't know if there's any data about this. But I think what would be a good study is the level of native proficiency in languages around the world.
Does languages considered simpler result in a greater mastery by the general population?