I would welcome a world where copyright restrictions ended 15 years from date of creation as this paper suggests, which would be a huge improvement from the status quo. Sadly the paper only seems to go over copyright.

But take the 3D printer example. Development by my subjective take seemed way more effective without patents. So why have them at all? More people did more work on them after the patents expired. Why have any period of limited growth if there will simply be more growth without the restrictions?

Well, I haven't proven completely that this concept is universally true, but I worry that "playing it safe" and just fighting to keep shorter restrictions is like loosening the rope around your neck when you really should remove it.

And your paper suggests they have a really nice formula ("99% confidence interval") for calculating the optimal term. But how would you calculate the optimal term for patents on AIDS medications during the height of the AIDS pandemic in Africa in the 1990's.[1] How much is each life worth? I question anyone who thinks their formula can calculate optimality on figures alone.

[1] https://www.mmegi.bw/features/the-neoliberal-plague-aids-and...

EDIT: I should underscore that there are a lot of natural reasons why someone would be in a position to invest in a particular innovation. We say we love free markets because natural incentives work best. No constraints but the laws of physics. IP restrictions are very unnatural.