If thinking/understanding/reasoning/whatever can be fake, it should be testable. It should be a conclusion that can be reached from results not baseless speculation. I mean, what kind of huge difference can't be tested for ?
If you tell me "this is fake gold" then there are numerous ways to distinguish fake gold from it's real counterpart, mostly by testing its physical properties.
If the results and properties from "fake" [insert] and "real" [insert] can't be distinguished then well you've just made up a distinction that doesn't meaningfully exist.
I agree with everything else you said, but this is a point I disagree with.
Just because something isn't testable, doesn't mean it doesn't exist. Theoretically, the state of facts could be such that 1) human minds can think (as in, have consciousness and perform the process that is known to us as "human thinking") and 2) machines cannot think (as in, they don't have consciousness, but are literally just mechanisms that appear to provide same output as humans for a certain set of inputs).
I don't think it's true, in fact, I don't think consciousness itself is anything more than a convenient illusion, but I still must point out that "what is real must be measurable" is not a valid argument.
A more precise formulation might be "if thinking can be fake, the only way we can prove it is if it's testable - otherwise it doesn't make sense to discuss it".
If it's not distinguishable then there's no difference period. Of course that won't stop people from making up differences.
An argument stemming from "well humans could have this special sauce that machines can't have...just because", is not something to take seriously.
It does not mean they are (or work) the same way.
That's true only if you believe that the world only exists inside humans' minds.
If you believe in objective reality, then things that are different but not distinguishable by humans can exist.