Newman essentially says that a high walk rate for a prospect, although indicative of good hitting skill, also signals a reduced ceiling because they don't have a lot of room for improvement.
It's an interesting argument, and I think one that holds merit. It also signals that saber based prospect evaluation that rewards strong plate discipline may at the same time be over-valuing it.
"On one hand, it’s great to see a young player with advanced plate discipline for his age and Flores certainly has it. On the other hand, that walk rate also forces me to wonder where the room for growth is?"
"If Flores is already able to identify pitches to drive and work counts to his favor, then his projection becomes much more dependent on physical development. ... As he advances, pitchers will challenge Flores more with fastballs and force him to hit his way through the upper levels as opposed to drawing walks due to his simply not being viewed as a hitter who will do damage. With a good base of hitting skills to work from, Flores is off to a fine start, but walk rates in Flores’ case may not be quite as valuable an indicator of success as many will assume."