Patents can be useful as an incentive, but their length need to correspond with the pace of progress in a given field. Otherwise, they end up slowing down everyone.

Once you have proven the need for an exclusivity grant, You also need to prove that 5, 10, 15 years of exclusivity via a patent would be unable provide enough incentive, that it had to be 20 years to strike the proper balance

In today's fast moving society, I think 5 years would provide more than enough incentive even for expensive technology that requires lots of capital investment though I would favor a shorter exclusivity grant, and then may be longer required licensing grant. like 2-3 years of exclusive use, and then 10 years of licensing but the patent holder is required to treat all uses of the patent in the same manner with fair and non-discriminatory pricing.