"I, like so many others, have found that it is rubbish at being a proper laptop"
Because you are trying to use it like you have been trained (and brainwashed) to use a computer. Users should not have to think about filesystems and such manual tasks.
"supports a mouse, has a proper filesystem, and has a reliable multitasking environment"
Again, you are thinking in terms of what you expect a computer to be. Like in the past when Apple killed the 5 1/4" floppy and used the superior 3 1/2" hard-case disk - outcry "Mac isn't a real computer". Then Apple killed the floppy altogether - oh you can't have a computer without a floppy.
Again Apple has shown it is innovating, far beyond what most people's indoctrination in how to use a traditional computer.