Whomever compared Castro to Hanley clearly believed way too much in potential. Castro hit a total of 6 HRs in 845 PAs in the minors. For that matter, Castro stole a grand total of 38 bases in the minors while Hanley stole 55 in his first 700 PAs in the majors. Frankly, their minor league numbers tell a tale of two very different players. Honestly, Castro has more in common with Yunel Escobar in the minors than Hanely. Castro is basically Escobar with average speed.
So, when we talk about prospects you have to consider the tools. If you have a prospect who has already shown plus plus power and at least average contact he's generally considered more valuable than a guy with similar make up only speed instead of power. In Baez's case, he's currently still at SS which basically never sees plus plus power. It remains to be seen if Baez stays there. And I've been very vocal about my concerns about Baez K rate and how he's a big bust risk until/if that doesn't get fixed. In Castor's case he showed average speed with plus contact but next to no power. That makes for an average to above average at best SS. Castro was never going to be Hanley at his peak or even Tulow for that matter because he flat out doesn't have the power. Until that changes, if ever, he isn't on the same level as a Baez type prospect.
For that matter, we should also talk about the difference between Baez, Bryant Almora and Soler. Almora isn't even close to the same peak as Baez because like Castro he doesn't have the power. Soler is rated lower because he plays a corner outfield position as well as the fact there are concerns about his ability to adjust to pitching throughout the game. Bryant and Baez are probably quite close in terms of hitting ability IMO. However, Baez is shakey to stay at SS and worst case goes to 3B or 2B. Bryant is shakey at 3B and may end up at a corner OF slot. That gives Baez significantly more value at this point.