> Observed reality/experience -- which is what the author invokes -- is not "first principles" though.

You're missing a huge point though, which is the difference between "observed reality" and calling out BS.

The author simply says that all these other things should happen if the hypothesis is incorrect, without any experimental data behind it. There is no evidence behind his assertion that all these other things should happen, so he's reasoning from his life experiences and his personal biases.

>The author simply says that all these other things should happen if the hypothesis is incorrect, without any experimental data behind it

That's still not first principles though -- not in the math/logic sense.

It's just things he doesn't bother to justify because they are well established.

A new paper in Physics doesn't begin by trying to prove the relativity theory or to give citations that show it's true: it just takes it for granted.