Most everything is derivative. It's not possible to be uninfluenced by copyrighted material.
Unless you can demonstrate, how copyright makes such influence illegal — and the development of various music genres proves the opposite — then your above sentence is irrelevant and does a disservice to the argument.
Also, how is it remotely fair that the IP owners can perpetually reap income from work that was performed even 10 years ago let alone 70?
As long as people still want to hear it, read it, or otherwise use it, then the creation was particularly useful and you (or your ancestors) should continue to be rewarded for it. Seems just as fair as your ability to live in the same house or swim in the same (privately-owned) lake for many years.
Most of us get paid once for the work we do.
Because most of us work for somebody else. We sell the results of our labors in advance to the willing buyer (employer) — and do not own it. Now, what we do own, we get to use (and profit from) for ever.
IP does not exist. It's a figment of our collective imagination.
All property rights are a social construct — and some even consider it to be "theft". If you aren't going to advocate that self-denying point of view, then your whining about Intellectual property is just as irrelevant...