Well, yeah, it's a thought experiment. But if we had some sort of ideal box then yes, the cat would actually in a superposition
"It's a thought experiment" means "we can specify a totally ideal box." It doesn't mean "a finite metal box on a table will actually behave this way."
I think that ends up confusing people a lot of people who can relate to the scenario, but don't understand that Schrödinger was accentuating the absurdity of the concept of superposition.
I really think that if the Cat was not a Cat, and if the binary was something other than the accessible-but-complicated concept of alive/dead, the thought experiment would be more useful to those of us who were not in the original messageboard threads between Schrödinger and Einstein.