This idea to me is absurd, especially to call it common sense
You're right. The idea that it was easier to land on the moon than to fake it isn't common sense. But it's true.
In the context of the time, rocket technology was far far ahead of film technology. It was technologically impossible to fake the moon landing in 1969. But it was technologically possible to land on the moon. Armed with just that knowledge alone, you can make the logical conclusion that the moon landing wasn't fake.
Now, the only reason this conclusion doesn't qualify as common sense is because the technology disparity isn't common knowledge.
In the context of technology today, it would be easier to fake the moon landing. But we aren't talking about today. We're talking about 1969.