It is a fact that our cameras have a built-in ability to respond to light levels differently. We can see it easily. In the case of film, there were clear physical differences between and within types of filmstock that directly impacted the physical ability of the film to respond to exposure to light. There were also clear chemical differences related to different processing materials and methods (primarily time and temperature, but not limited to those factors) that further defined how many of which grains of silver in the negative and paper turned darker.

In the case of electronic cameras, there are very strong parallels to chemical photography. Processing and application of the semiconductor materials used to produce the sensor have a similar effect as the physical characteristics of the filmstock. Electronic processing of the signals coming from the sensor roughly parallels the chemical processing of filmstock material. At the core, these reactions and processes are both similar and different. But it's very difficult to see how that render efforts to classify and scale usable sensitivity to light as fake, since turning the dial and changing the set sensitivity does make a difference in the final image that is very similar to the difference in negative density coming out of a processing bath.

So...different? Yes, absolutely.
Fake? Absolutely not.

Before you tell me not to listen to this Tony guy let me explain. He has the controversy topic of crop sensor which caused a lot of disagreement but I don't want to talk about that. His latest claim that ISO is fake and I email him asking him to do a test of his cameras and see if they conform to the ISO standard and heard nothing back from him.
I don't see how ISO is fake because.
1. The ISO organization is real and based in Switzerland.
2. There is the ISO standard for digital still cameras and the latest is ISO 12232:2019 published Feb 2019.
3. Unless you test the cameras against this standard and they don't meet the standard then you can't claim that they are fake.

I just read the condensed version (didn't want to pay 118eu). It looks like a set of "guidelines" that give manufacturers a bit of latitude. In one other place (can't remember where), I read that base or native iso was based on the value obtained when the sensor reached saturation. But, how does that account for the difference in base iso's - everything from 64 to 200? I don't know I'd call iso's "fake"; but, from here, they sure look like they're somewhat arbitrary.

In the end, is it a big deal? We know that, at some point, noise becomes unacceptable for a particular type of image (landscape, street, wildlife, etc.); for the photographer and, perhaps, a knowledgeable viewing audience. I know where those personal unacceptable levels are for my camera for landscapes and wildlife and I assume every photographer reaches a point in their experience level that they know as well. That still doesn't keep us from stretching or exceeding those levels when there's a "moment" we want to capture noise be damned.

I just read the condensed version (didn't want to pay 118eu). It looks like a set of "guidelines" that give manufacturers a bit of latitude. In one other place (can't remember where), I read that base or native iso was based on the value obtained when the sensor reached saturation. But, how does that account for the difference in base iso's - everything from 64 to 200? I don't know I'd call iso's "fake"; but, from here, they sure look like they're somewhat arbitrary.

In the end, is it a big deal? We know that, at some point, noise becomes unacceptable for a particular type of image (landscape, street, wildlife, etc.); for the photographer and, perhaps, a knowledgeable viewing audience. I know where those personal unacceptable levels are for my camera for landscapes and wildlife and I assume every photographer reaches a point in their experience level that they know as well. That still doesn't keep us from stretching or exceeding those levels when there's a "moment" we want to capture noise be damned.

Before you tell me not to listen to this Tony guy let me explain. He has the controversy topic of crop sensor which caused a lot of disagreement but I don't want to talk about that. His latest claim that ISO is fake and I email him asking him to do a test of his cameras and see if they conform to the ISO standard and heard nothing back from him.
I don't see how ISO is fake because.
1. The ISO organization is real and based in Switzerland.
2. There is the ISO standard for digital still cameras and the latest is ISO 12232:2019 published Feb 2019.
3. Unless you test the cameras against this standard and they don't meet the standard then you can't claim that they are fake.