Nobody truly knows how these prospects will pan out, I like to think of prospects as lottery tickets (yeah, a bad example talking about actual people but whatever lol) with the higher end prospects giving you a larger chance of hitting. But hey, if you have a 90% chance of hitting it big you still lose 10% of the time, and if you have a 99% chance of not then 1% of the time you do hit it big. We have Lars Andersons and Rusney Castillos and we also have Mookie Betts and Xander Bogaerts too. It's just the way of prospectetum.
One thing I recall recently is on a past Soxprospects podcast (I think about a year ago), the staff there talking about how they thought Duran was being over ranked by the national media, and they (who had the most eyes on him) where not as high on him. They always kind of pegged him as a 4th outfielder type, maybe more if he ever put it together and he could be a bat first LF type. They also compared it to the time when the national media was much higher on Lars Anderson than they were on him too. Even the best scouts are going to be wrong, A LOT, but I trust the guys who have the most eyes on players. I will say this, the guy who they think is being overhyped now is....Rafael Caddenne, who people think is going to be the next Mookie Betts, but I think a more appropriate ceiling for him might be Kike Hernandez, and that's still really really good.
You're right about Casas, I do however have a higher degree of confidence he's going to pan out but nothing is guaranteed until they're there in the bigs doing it. I actually think Casas has the ability to hit better in the majors than he does in the minors, I think his true power doesn't show because he's so patient and pitcher seldomly challenge him. We shall see.