The problem is that you don't know when the 15% comes into play. You can't win if you don't play. BTW in 2016 when we didn't have a 5th pick the Steelers traded for Brandon Boykin. How well did he do? Like I said. It's not a big deal but it still makes moving up and finding gems later on more difficult.
It also doesn't take into account whether it is an early 5th or a late 5th, it makes a big difference