I reckon that more returned players work out than kept players, it's just that we remember the kept player success stories. I also bet that the rate of success for returned Rule 5 players is no worse than the rate of success for all minor leaguers at whatever level they'd reached before being taken. Because it's not high for anyone.
So who do we think is more likely to end up panning out for the Phillies from here, Abel or Castellano? They are the same age and began their pro careers the same year.
Inciarte and Vic are both good examples of guys who got the additional seasoning they needed, though Vic had already been taken and returned in the Rule 5 before (probably why the Dodgers cut bait the second time). I always thought Tyler Goedell might have had a better career if he had been returned.
And then there is Herrera who was just unique. He'd already repeated AA so he was more MLB-ready than your average Rule 5 guy. And nobody saw the position change coming. The Rangers didn't need him as 2B and they also went and got DeShields Jr. in that same rule 5 (ahead of the Phillies pick).