You do not play the best to be the best.
You play the schedule that makes your team the best.
If you play plenty of tough games, and if you have difficult league games, it is pointless to pound your kids every time out. There are a lot of reasons, but here's one thing I feel I've learned over the course of my coaching career: The most important things to have heading into postseason are health and enthusiasm.
If you play physically challenging games every weekend in January and February, plus your league games, you are likely to be physically drained in the playoffs. If you play too many "big" games, the kids get tired mentally.
I've had some very good teams, and been an assistant on better ones, and it would have made absolutely no sense for us to have scheduled the best teams we could find in every available non-league slot. It would have been suicide, both for our record, our chances of advancing in postseason and for our players' health.
The reality is that the more wins you have, the higher you will be seeded, and having played a really good D4 team in December isn't going to do you a lick of good in March -- unless you lost, in which case you might be on the road against a good team instead of hosting.
Now, if your goal as a coach is to play as many good teams as possible, regardless of wins or losses, then indeed play the best, and play them all the time. If so, you better have at least three D1 players and lots of depth because otherwise you're going to lose a lot of games, get a bunch of kids hurt and wind up either on the outside of the playoffs or traveling to a top three seed in the first round.
I've never had a team good enough to play SMS, SMB, SI, O'Dowd, Berkeley, Mitty and every other quality team in the same season, but by your logic I should do that every year, I guess. That way we'd be our best, is what I'm hearing you say.
If you have a state-title level team, that elite schedule makes sense. If you have a league-champion level team, it would be foolish to play those teams. Losing by 40 every time out does not make you better (trust me, I know that from experience). You should play the teams that challenge you, absolutely, but you need to win a few games here and there or nobody has a good experience. I've never bought the idea that going 4-22 against the best teams is better than going .500 against teams you can compete against.
You do not have to play the best teams to have your best team. There's a lot more to it than that.