There is nothing wrong with "copying" kernel. This is what the open source is aimed at: Infectious growth. In fact that was the right and smart thing to do.
I think you might be unfamiliar with 'open source' and its licensing. Android is a Linux-based distribution, which means that it uses a Linux kernel.
'Copy': make a similar or identical version of; reproduce: [1]
Google forked and contribute to the kernel. They did not create their own identical version of, or reproduce, the kernel.
"Forking" does not necessarily mean "innovation". Innovation, by definition, requires something new. "Doing the same things differently" is only innovative to the extent that things are done differently. (Android certainly did do some innovative things, just saying that forking the kernel was probably not it.)
Yes, but reinventing the wheel is not innovation, it is stupidity. Why write a new kernel if there is a very good one available? Innovation often is in taking existing things and combining them in new ways (or improving already existing inventions, which is what google is doing).