Very good analysis; I think you've hit on some of the major challenges of coaching youth soccer.
I totally agree...soccer success should be judged on a continuum, and I feel lucky to have had many parents who can see progress over the course a season (and even multiple seasons). It's not reasonable to try to "fix" things instantly in the game, because as you rightly said, the coach doesn't (and shouldn't) have the kind of in-game control as in many other sports. We don't call plays, we don't have time-outs, we prepare our players as best we can before a game, we support them as best we can during the game, and we plan how we can further prepare them between now and the next game. If we're really doing it right, we're working toward making them into better players and a better team in the long haul, not just trying to win in the moment. In the game is not the time to "fix" things that haven't been addressed in practice; that causes confusion and frustration.
I agree on setting the expectations and ground rules early; helping parents and players to understand from the start what you're doing, how you plan to do it, and why you plan to do it that way can help to avoid the misunderstandings when the coaching they're seeing (or often NOT seeing) doesn't always match what they're used to seeing in other sports.
