As others have noted copyright duration is ridiculous. But more importantly it lacks severe counter-forces to balance out the explicit monopoly.

Since the point of copyright is to offer an incentive (to profit) from works it should be tightly tied to the market value of said works and the willingness of its owner to present them for sale.

If nobody keeps selling X there's no reason to let X enjoy the protection of copyright.

If X is kept for sale for the sake of keeping copyright alive but it's not really selling much that should also affect the nature of the copyright. For example, a minimum fee you have to pay annually to keep copyright going would cull out the works that are no longer commercially viable.

The fee could be proportional to the overall sales of the works so that if your works were a huge hit in the 80's but sales have trickled down to a minimum you'd have to pay more (from the profits you've obviously received over time) to keep it copyrighted (which would force you to balance your copyrights to your net income from current sales), but if you published an obscure album decades ago that never got much traction your fees would be negligible (but you'd still have a minimum fee you'd have to pay regardless) so you would be incentivized to give up the "protection" and make it cheaper for everyone to let it fall in public domain.

Further, the various aspects of copyright could be torn down in different timeframes. Let's say you wrote a successful book in 1963 which made money but no longer sells much. You probably wouldn't mind letting the copies of the book fall in public domain but if you could keep the option to hold onto copyright for derivative works in case someone wants to make a film out of the book you could do that (again, with annual fees, but these could be lower if the original book could be freely copied).

Or some other scheme. I could soon think of dozens if I wanted to but you get the idea. How about a tax on the sales of copyrighted works that starts from 0% but increases by some percentage point each year. You can profit first but as years go by you will have to start paying more and more to keep it going as the overall balance approaches unprofitability.

Copyright doesn't have to be a complete monopoly, it could have shades of gray. Sure there are exemptions already (such as fair use, in some countries, or right to make backups under certain conditions) but none of them address the commercial stronghold copyright allows for companies to keep works of art hostage for decades and eventually, for centuries.