That can be equated to working out in general. One can get in great shape by just "doing stuff" - chopping wood, playing sports, etc. - but you can't get in the same shape as if you were to go to the gym and work out with free weights, doing an inverted leg press of 700+ pounds, or benching 200+ pounds. In the same vein, one can become proficient at guitar by just learning/writing/playing songs, BUT they will not be as good as someone that not only plays songs, but also "lifts weights" be pushing the envelope of their technique with sweeping, scales, chromatic exercises, alternate picking, etc. See what I mean? One thing you are right about, though, is that when doing exercises, you have to keep musicianship as your #1 goal, not technique for it's own sake...