Great thread. Gets you thinking. As my 2017 deals with HS and travel umpires of widely varying quality and consistency, being inconsistent is the norm. Many of that "class" of umpires it seems love to "punch-out/ring-up" a non-swinging batter on a full count, or any other count with 2 strikes. So, sitting on a 50-50 ball on a full count and hoping for the ball/walk does not seem to be a good idea. But I have no data to suppory my statement. I agree that, in theory, and especially with better/more consistent umpires, a strong case could be made to take on a marginal pitch.
As others have noted, recognizing a 50-50 pitch when 1 strike away from sitting can be challenging in itself. I'd say hacking at a close pitch on a full count might generally perceived in a more positive light than getting a backwards K.
I am going to guess PG is talking about the more experienced umpires than you might find at a your typical 13U tournament. In my area a HS game is worth $70+ while a 13U is worth $35 or $40.
It is a winnowing system to get to the higher level's of baseball for the umpires as it is with the players.
One other factor. HS has 1 game...13U tournaments you can catch a guy doing his 4th game of the day. On a 90 degree humid day is anyone surprised his zone might be bigger than it might normally be?
These things are accounted for in good showcases and HS leagues and I think that is the level of ball this thread is focused on.