Sounds too simplistic and divisive, yet on the contrary, Ferguson did a well-balanced of both still winning and rebuilding/developing players.
Not including the C92, there's O'Shea, Fletcher, Rafael/Fabio, Evans, etc. That's just from our youth. Examples can also be made of us buying young players who haven't developed yet when they joined eg. De Gea.
Counter argument can also be made that's SAF, post-SAF is different... and yet, LVG and Mourinho still won things with a mix of both established players and young players.
Doesn't have to be just one of the two ain't it.