[Breza]

You just nailed the difficult balance in copyright law. I agree that life+70 is wayyyyy too long. But you also want to incentivize creators to keep trying to make something of their existing IP. Sapkowski is one example. Another good one is the Dresden Files series, which is 26 books in and still going strong. Each book in the series repeats some of the basics that were covered in the original (often using the exact same phrasing). Then the author extends the story over the course of a few hundred pages. If the original book were already public domain, anybody could write a fairly convincing in-universe book and I have to imagine the author would have moved on to other series.

Personally, I think 50 years strikes the best balance. Everything from the '60s would be fair use, so Spiderman would be public domain but not a wizard named Harry.