You're right that it's more consistent to have windows behave as you describe, and Windows and Linux both treat fullscreen windows this way. I posit that Apple cares more about not hiding windows behind others than it does consistency. This also shows with their new window placement algorithm that results in an absolute mess of windows all partially occluded but with some corner or edge peeking out of the stack for a user to visually identify and click to focus/being-to-top. Compare to Windows that (at least when I last used it) opens new windows at a slight diagonal offset from the last focused window, almost like building a neat deck of cards. Apple's ethos is also on display in the design of Stage Manager, which groups windows into these messy clumps and creates a visible shelf to swap between window bundles. Everything is optimized for hunt-and-peck visual users. If you're the type to organize your windows and workflows then you're fighting the system.

If you click the full screen window, your little window is now behind it…