Just for fun, I went back and looked at the top 10 LHP/RHP pitching prospects at the end of 2015.
RHP:
1. Lucas Giolito (near bust)
2. Tyler Glasnow (opener/long man?)
3. Alex Reyes (electric stuff if healthy)
4. Jose Berrios (pretty good, has potential to be even better)
5. Jose De Leon (hasn't pitched since 2017 due to TJ)
6. Jon Gray (a trade away from being good)
7. Robert Stephenson (can't throw strikes)
8. Archie Bradley (saved by the bullpen)
9. Carson Fulmer (terrible control)
10. Mark Appel (out of baseball)
LHP:
1. Julio Urias (injured, but could very well still pan out)
2. Steven Matz (good, but durability concerns)
3. Sean Newcomb (pretty erratic control)
4. Brian Johnson (already 27 and has been a spot starter/long reliever)
5. Blake Snell (ace)
6. Tyler Jay (shifted to bullpen, left unprotected in the Rule 5 and still goes unclaimed)
7. Amir Garrett (chances are he's a bullpen arm)
8. Robert Kaminsky (who?)
9. Kolby Allard (jurys out)
10. Sean Manaea (solid mid rotation guy with #2 upside on a good year, but just got TJ)
So out of those 20, you can argue only 5 have panned out (Manaea, Snell, Matz, Gray, and Berrios). That's a 25% hit rate on even the best arms, and only one that became an ace. Ouch
You compare that with the Top 10 SS prospects here: http://m.mlb.com/prospects/2015?list=ss
You could say at least 5 of those guys have panned out (depending on where you land on Dansby).