While I completely agree with everything you say -- especially regarding HS performance -- it's interesting how a player's future DOES sometimes seem to be significantly impacted -- positively or negatively -- by how he performs on certain stages that offer REALLY small sample sizes: particularly non-pitchers.
I'm thinking of a guy getting called up the the Bigs, for example ... who gets maybe 30 or 40 at bats, and really struggles, or vice-versa. Or a guy who kills it at a PG national event.
Obviously there's a body of work to look at in these and similar cases, and scouts do ... but sometimes small sample sizes do matter, don't they?