My son played with Christian Yelich at the first showcase for either of them. Christian was rated a 7.5 out of that showcase. We got a laugh when my son was rated a bit higher, but pitchers are a bit easier to rate. Christian didn't get a hit during the showcase and made some pretty poor swings against both soft pitching and hard pitching. I didn't see his BP, but his dad said he did pretty well. He ran fairly well but his arm strength was to put it kindly not evident and his throwing motion is a bit on the funky side to boot. PG saw something there to give him a 7.5 rating. We've known him from PONY league days and know that he's got one of the sweetest line drive swings you'll ever see but it wasn't evident at the showcase. PG has to go on what they see. Christian was rated much higher in short order but on the basis of his first showcase 7.5 was a generous rating to someone who had only seen him perform at that showcase. PG is pretty good at projecting but the kids have to show up on that day.
As far as the original question an 8.0 is pretty good but all it will do is get attention. The player will still have to perform in other situations. Showcases are a start but players actually get signed out of the big WWBA tournaments because the scouts/coaches can see them in a truly competitive environment.