Apologies to you because my criticism isn't aimed at you, but at the author. That article is garbage. "Trades of highly ranked prospects are super rare! But here's a half dozen that have happened in the last couple years...."
And why list their ranking after the trade? Noah Syndergaard's preseason rankings three seasons after he was moved means dick to the premise.
I disagree. All of the top-10 prospects since 2000 is something on the order of 160 prospects (something like because some guys will have made that list more than once before aging out). I'd imagine that that's a lower rate than, say, all prospects listed in the various Top 100 lists, but I'd love to actually see numbers to see if my intuition is well placed.
But I agree that they weren't necessarily setting the bar at the right place. You'll note that Maybin (3, 5, 6), Myers (4), Kazmir (4, 8) and Russell (5) are the only ones who peaked higher than 9. Prospects in the 9-30 bin (guys like Hanley Ramirez, Andrew Miller, Jesus Montero, Andy Marte, Trevor Bauer) seem to be dealt pretty frequently; the guys more highly regarded than that are dealt much more rarely, in the kinds of deals that we still talk about years later.
So, really, Dansby Swanson is more like at the high end of the kinds of trades that do happen pretty frequently.