Twenty years to hold monopoly production rights is an obscene amount of time.

Yes, reducing that twenty to say five will reduce capital investments in drug research, but it will also alter the structure of those investments.

Investing in improvements at the margin might make sense when you can collect 20 years of royalties, but if you can only collect 5 then it'll more often make sense to fund cures and use that 5 year monopoly to cure as many people as you can before the drug goes generic.