GUI-based system still needs command shell or it will lose a lot of flexibility arising from being able to evaluate small bits of code and therefore code incrementally.
"If you have an x86 machine without an operating system on it, is it a computer"
No, it's a pile of iron and silicon.
"Is an iOS device not a computer because it doesn't have a CLI?"
Not after you buy it, you have to turn it into a computer.
"What about a hypothetical computer that uses your brain as input - would that have a CLI?"
It sure will, how else will you use it?
It's not pedantism. Pedantism is about meaning of words. My rant is about meaning of concepts. If you hit nails with your microscope, it's not a microscope for you but rather a lame hammer.
Is an iOS device not a computer because it doesn't have a CLI?
What about a hypothetical computer that uses your brain as input - would that have a CLI? CLI/GUI/etc is irrelevant to the definition of computer.
Unless you're just being a pedantic troll, in which case kudos :)