That was not the ruling, no. But that was the effect.
"In essence, he declared that Madison should have delivered the commission to Marbury, but then held that the section of the Judiciary Act of 1789 that gave the Supreme Court the power to issue writs of mandamus exceeded the authority allotted the Court under Article III of the Constitution, and was therefore null and void."
The USSC ruled that a Congressional Act was unconstitutional. It positioned itself as final arbitor.
"So who was the final arbiter of the law in that instance, FDR or SCOTUS?"
As you know, SCOTUS caved.
First of all, those words were written by a very liberal writer in 1994, just a bit more than 14 years after the ratification of the Constitution, and at a time when I'm pretty sure none of the original drafters were around to comment on it. Secondly, nothing in that statement says anything to the effect that SCOTUS is the final authority on the meaning of the Constitution.
As you know, SCOTUS caved.
So what are you saying? That anyone who can force his will on the law is the final arbiter of the law?