The kids care and know if they won for not. I've seen this BS argument for so long in soccer - we're developing players, we don't care if we win! Well, if you are doing a better job than the next coach, you will win. It's such a dodge of responsibility. In no other sport in the US does anyone say 'we don't care who wins'. You have 10 - 12 years olds in Little League mastering the game - but at 10 in soccer we don't care who wins? More than a few years ago now, we had NCSL as the dominant local soccer league, but it had promotion and relegation, which required you to - horrors - WIN to stay in your division or else face relegation to a lower division. That league is now basically a shadow of what it was, so everyone can play in leagues that just require your check to clear.
I don't understand your point in the context of OP's post Winning is important so it is better for a coach to get players from elsewhere to give the appearance that his team won even though it wasn't his players who contributed to the win? Your argument might make sense if coaches were consistently training and playing he same group of players, not routinely adding and subtracting players to produce wins on any given day.
Tournaments are tiered. A good club/coach puts each team in the appropriate tier. If the team has no chance of winning without the guest players, then the coach isn't doing is job and the "win" is a cover.
Maybe my kids are weird, but at that age, the would have much rather played than won sitting on the bench.