What a completely absurd statement.
The rationale for 5000 page bills is for congresscritters to hide behind and not read before voting for them. And to make them inaccessible for the citizenry to grasp, so as to direct their congresscritters their viewpoints.
So, to put an arbitrary stake in the ground, for lack of any other, I’d go with the size of original law, the Constitution itself, as the red line beyond which no bill should extend.