This was adjudicated up to the Supreme Court: https://www.oyez.org/cases/2002/01-618
tl;dr: 7-2 as long as there is some type of time limitation, Congress is free to extend copyright terms.
tl;dr: 7-2 as long as there is some type of time limitation, Congress is free to extend copyright terms.
This is a good point worth bringing up, since the GP seems to imply it isn't with reference to the wording of the constitution's Copyright Clause.
However, it doesn't answer the moral question of whether congress should have passed that law, or whether congress should pass laws to change copyright term lengths to be shorter. That's not the role of the court.
Presumably SCOTUS would say that an effectively-infinite timeline is not "limited" within the Constitutional definition of the word. Eldred v. Ashcroft basically tried to argue that continual decades-long extensions amounted to this, but the Court was not convinced.