If copyright at life+70 years oversupplies the art market, crashing the equilibrium price to nearly zero.... Is the solution too obvious? Cut the term of copy

If copyright at life+70 years oversupplies the art market, crashing the equilibrium price to nearly zero.... Is the solution too obvious? Cut the term of copyright protection by 5 years every year, then start halving the remaining term after hitting five, until the shovelware "art" becomes trivially manageable. If it still comes in heaping, steaming piles all the way down to one week, then clearly copyright was unnecessary.