Yes, I think in most ways we're in complete agreement, Bum, but maybe we are focused on different sides of the scout/prospect equation. As you say, scouts need to be concerned with the actual performance level of the prospects in front of them.
There is always an implicit comparison being made by experienced scouts: The prospect in front of me vs. the average performance expectation at this prospect's level. Smart, experienced baseball people can readily match up a prospect's ability with the average expectations at that level...I think that works pretty well. Mistakes are sometimes made with the intangibles...character, heart, etc....but performance can be accurately judged by experienced coaches/scouts....there's little doubt about that.
The biggest problems in matching personal ability with realistic baseball level doesn't come from scouts and college coaches, it probably occurs mostly on the side of the less-experienced HS-aged players and/or their parents. On that side of the equation, accurate quantitative data can be helpful for putting things in context and setting realistic personal goals.
What's cool about Perfect Game data: It's very extensive, objective, and very accurate....so it tends to shed higher quality light on some baseball truths that are often discussed in very fuzzy ways by highly opinionated folks with questionable experience...(this is a mild jab at the internet in general, not at any specific persons...and it's certainly not a jab at Bum, whose baseball insights I've appreciated for years).
As an extreme example, if the average velocity in High School is 91.5 mph for the RHPs that eventually showed up on UCLA's 2012 roster (it actually is!), then you may want to reconsider your chances to realistically pitch for the Bruins if your velocity as a HS junior is topping out at 85 mph. Even if mom & dad are UCLA alums, your grades are outstanding, baseball is your life, and UCLA is your dream....you should probably re-think all of that stuff if you top out at 85 mph as a HS junior. The numbers do reveal pretty clearly and specifically what UCLA's program expects from its High School prospects.
That may seem way too obvious of an example to people with loads of baseball experience...but, it's only part of an important point:
Even if he is not projected to pitch for UCLA, for example, there are still lots and lots of places in the D-1 spectrum where some HS kid topping at 85 mph in his junior year would be projected to have a completely legitimate chance to play, if he wants to. Perfect Game data, when it is properly used, can help HS prospects and their families find some of the less-than-obvious answers, too.