The way I interpreted the summary was people who participated are basically paying for the depreciation of the device, which with Apple I would expect to be far less than half the device's cost.I went from a 6S to a 13 Pro and the performance of the 6S was pretty dam good still. It was all the other improvements added together that really had the biggest impact.
I still think owning your phone outright then selling it will be a cheaper total cost of ownership, plus you aren’t leasing a phone.
This could benefit a lot of people since more refurbished devices could be offered to people who don’t see measurable benefits from generational updates to performance.