Two points:
1) The rationale behind mandated formations (at least at the youth level) is to de-emphasize the coaches tactical role and to allow players to focus on learning the game.
How often do you see one U12 team trying to play an attacking-possession 4-3-3 get creamed by a 4-5-1 with a physically more mature forward that receives long ball after long ball?
If development is the goal, then mandated formations make sense. If you have been trained in an environment that encourages understanding roles/space - then when you move to a results based environment (professional), you can play in whatever formation is required.
2) A formation is just a tool. Even teams with a more rigid/organized mentality will shift in and out of different formations depending on the situation. A team can play a "4-3-3" but maybe it's a 4-3-3 in attack (could even be a 4-1-5!) and a 4-5-1 when they don't have possession.
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It's an interesting debate, but I think you have two separate debates depending on your perspective (competitive-professional or developmental-youth).
