That argument it's not the reason why IP exist. The justification is that IP will create more value for society through incentives, not that the inventor would loss value. Otherwise you could justify eternal IP.

So, the only defense for IP is "it creates more value for society than the alternative". If we look into it, and the alternative is better (I don't know), the inventor should loss their privileges.

IP is not a right, it's a monopoly, a privilege given by law, and can be changed by law if judged not convenient anymore.