1. Unless they are really elite bullpen arms, yes they do grow on trees. Smart teams pick up arms like Greg Burke, Pomeranz, Miguel Gonzalez, Luis Ayala, and Miguel Socolovich for next to nothing every year.
2. Guess we have different definitiions of dominate. Schrader had a 1.32 WHIP at Frederck. As for that little growing pain at Bowie, 24 BB's and only 17 strikeouts in 23 IP, just show that he has a long way to go.
3. Belfiore was 23 this season and after dominating the Cal League (0.94 WHIP 2 walks 28 K's in 19 IP) his numbers were DECENT at Bowie (1.35 WHIP 50 K's 21 walks in 47 IP). Those aren't dominant numbers. It gets tougher as you advance.
4. A mediocre starter in the minors with a good arm can be a dominant or at least a very effective reliever in most cases, That's why I think you are overrating both Schrader and Belfiore. I understand why you have them on the list. I just disagree.
Schrader has the potential to be an elite bullpen arm. Also guys like Gonzalez and Pomeranz are the exception not the rule. For every one of them, there are 5-10 guys that do nothing. Also Ayala has been an established RP before, I wouldn't put him in the same category with those guys.
It's important to not only look at numbers in the minors... You need to focus on their potential more-so than what the numbers are. Not saying that numbers do not matter (of course they do), but they are not the only chapter to a story.
Another thing on RP. The reason they can rate just as high is because they are fast moving and can have an immediate impact. They can help quickly and move up the ladder fast. It takes more time to iron out kinks as a SP, and in the bullpen a pitcher can get away with some flaws in their mechanics, delivery, and approach. Pedro Strop is a good example. Imagine him as a starter. He wouldn't last longer than 3 innings without imploding due to all the wacky stuff he does (Just a general example, don't look too much into me using him as it)
Also, sources I talked to while compiling this list had Schrader higher on their lists than mine. One guy had him top 10. Belfiore was anywhere from 20-15, so I don't think I am any higher on those two than anyone else.
This list was not just my opinion, I put some effort into talking to others with much more experience than my own so it was a more concise list.
There are a ton of RP I left off this list because they were a dime-a-dozen types. They have talent but just didn't do anything to separate themselves from the pack. Guys like Trent Howard, Matt Taylor, Ryan Berry, Josh Hader (although Josh is more due to him not having an extensive resume yet. He could absolutely make this list at midseason next year, but just want to see more before making that jump)
I hope what I am saying makes some form of sense. I can see why some would not want RP rated as high.