I do believe in hitting the ball out front, after getting to a balanced position (50/50, 60/40 ish) after stride and then staying behind the ball. At that point the ball needs to travel, but definitely not as deep as say belly button, by that time you are probably blown up. but you can't go out getting it either and be at the end of your extension. if you are balanced, head between legs, you don't need the ball to get so deep as you do if you are leaning back on your back leg, you are able to cover the outside pitch with good bat direction and path and still hit it fair say just inside the front knee. It's all relative to your position.
IF you lean back or collapse/tilt back then you have to get the ball deep, say back corner of plate in order to reach anything middle away. otherwise your bat is in and out of the zone too early, ie running out of barrel. If you go out to get it and are then too early, you are in and out of the zone, and lack adjust-ability to off speed.
I think in teaching you have to be really careful how what you say is interpreted, cues like Stay back, let it travel, hit it out front, all can mean different things to different players. You may need to tell one player to let it travel and another to get it out front, and often they end up being the same thing. You may need to tell a guy to swing down and another to think up, to get them to swing on plane. So I don't really get caught up in right or wrong when I hear the terms thrown out. But if the coach is just throwing the term/cue out there and not giving any context or reason, that is not good.
Getting the ball out front does not mean Pull.
Sorry for the long post.
As far as the original topic,, hitting oppo to develop power, I think working to stay inside the ball, stay on the ball, and get the barrel through the ball with direction are all things that during batting practice help develop power and result in going the other way... in my mind there is no debating that pull side is going to be far more power, but it's a trap. If you work to stay through the ball and happen to get a bit ahead, you will crush it pull side. But I think you develop far more bad habits trying to pull than working oppo during practice. But during games, I wouldn't force going the other way either, it should be a byproduct of pitch and location.
All fun topics I love to discuss.