LHPParent,
Players that participate in the PG National Academic Showcase will receive a rating from PG. Each players tools, not stat line, will be assessed by PG. No seal of approval...it's a rating, though some players will be named "top prospects" or receive other accolades. And no assessment of the stat line from any games that get played at the showcase.
And there will be coaches at the showcase. Are these the "right" coaches for your player? That depends as has been discussed in this thread.
Going to a PG showcase and getting that rating, will give you PG's very experienced assessment of a player. Yes, that can help guide you with what your player's "level of play" is. It will be one, very experienced opinion.
Do you need that opinion to provide the "filter for level of play"? If so, then by all means go. I would encourage getting multiple opinions, but PG's will be pretty darned good.
Those opinions (plus the opinions of academic/college advisors) will help your player fish in the right pond. Your family can build a vetted list of schools that is the intersection of potentially where your player can play and where they can be admitted. Then I recommend the player goes where the coaches on his vetted list will be, e.g., other showcases, camps, etc. And there's a bunch of other things a player will do to demonstrate interest in the schools on their list, e.g., visit admissions, visit coaches, fill out admissions and baseball profiles, send video, communicate frequently, etc.
Good luck!