We keep rehashing the same old stuff in this thread...
Our HS varsity team uses situational hitting. Our team takes a line drive approach, not a "lift" intent. We put a premium on line drives and discourage fly balls and ground balls unless situationally appropriate. We modify slightly with the outlier speed guy or true power guy. Currently, we are considered the best hitting team in a decent California HS league that regularly has multiple teams chasing the equivalent of state in our division. There is only one team in our league that has more extra base hits than we do. Yet, we have scored over 20% more runs.
Most good HS AND college programs I am familiar with use the same approach and I make it a point to be familiar with many. It is age and skill level appropriate. Hitting behind the runner is definitely not dead. We executed this in a key inning, as well as multiple bunts in another, just last night. I talk to college players regularly who are taught the same thing we teach and are asked to execute situationally similar to us on a regular basis.
If you are seeing "many many 14's who at least have the capability to hit the ball 350 to 400 feet", you are in a different world than I am and I'm in California where there is an abundance of good baseball. There are plenty of reasons why you would not want to teach a 14 y.o. to lift. How capable is he of getting the ball over the top and with what consistency? What will that do to his ability to keep the barrel on plane with the ball for an optimal length of time? Etc., etc. There are plenty of reasons to teach a HS player how to be successful today instead of just focusing on what he may be able to do at the next level or when they get much stronger. Here's one - Most HS players are not going to play at the next level. Their baseball lives, memories, experiences hinge on what they can do to succeed now.
I am very in tune to what sabermetrics is bringing to the table, what the resulting changes are and how it affects decisions at the MLB level. I am always trying to learn and keep up with any changes I should be making for my players. In many cases, what applies to MLB players and that game does not apply as best practice to other levels.
As far as hitting the back of the cage... you can youtube MLB and top college guys (with college, it is coaches with players) doing hitting drills in cages. Many of them clearly are intentionally trying to hit the back of the net, several even stating exactly that. As I've stated in previous posts, I don't dispute the 15 - 25 degree stats at the MLB level. But even many of those hits came about with the intent to just hit hard line drives. Yes, some MLB players swing with intent to lift. Not all. Doesn't mean it's what every HS player should do, or even most.