You take it with a grain of salt, and I think that you will really know the answer as to how good that class was after they leave- or probably even before then.
I saw the comment that I think you are getting at- where he said he puts more stock into them because they are compiled by professionals. I have to agree with you- it's still an inexact science.
At the same time, much like football, I think there is a probably at least some correlation between the schools that win and have good recriuting rankings. Our team has classes from three that were not ranked very high, and we're not very good. So, they're probably not totally off the mark either.
Also, with scouts vs college recruiters- they're looking for two different things to a degree. The scouts, as you say, are looking more for potential and are trying to project where a guy is going to be in 4-5 years. College recruiters, who don't have the luxury of four levels of minors to devlelop talent- are looking more for guys that can come in and play immediately at the college level. Of course that doesn't mean that the scouts don't know who is or isn't a good player as well.
But yeah, I saw that comment, and I don't think that I really agree with it.
As far as them being more of a shot in the dark- maybe- it seems about the same to me.