If you bring Soria into a game in the 7th during the regular season intending to let him get 7 outs, and you have games for the next 10 days straight after that, then you have to be prepared to win a different way for at least the next 2 games.

First, your point is valid and that is a concern, but I want to point out that bringing a closer — or “relief ace” — into a game in the 7th inning does not necessitate that he finish the game. Let’s say this pitcher comes into game into a tie game in the 7th and runners on first and second. That’s a pretty high leverage situation. Let’s say he gets two outs, allowing no runs, getting his team out of the jam. Then if the pitcher’s team scores a couple runs before the 9th inning, suddenly you’ve got a moderate-to-low leverage situation to start the 9th inning. Let some other pitcher (like the second or third best reliever) pitch the 9th. Then the relief ace has only pitched 1 2/3 innings and could pitch the next day if necessary, or just be rested for one day.

Second, I think relief aces should be used with a “bird in the hand is worth two in the bush” philosophy. If you’ve got a high leverage situation in the 7th or 8th inning, you’ve got a close, winnable game. In the next game or two, who knows if you’re going to have close, winnable games? You might have clear losses or wins in those games which wouldn’t be appropriate appearances for the relief ace. I rather use him when I know I need him, than save him for future games where he might or might not be needed.

Of course, the best way to maximize Soria’s impact on the team is to put him in the rotation.

This is always and undoubtedly true. The only thing that keeps me from saying that this is a colossal blunder by Moore/Hillman is that there is a valid concern about his mechanics. Independent analysts have pointed to Soria’s mechanics being an injury risk. If they (and Moore) are right, then there is a real and big downside to trying to have him throw 100 pitches in a game and 200 innings in a season (even after appropriately and slowly built up to this). I don’t know how great the risk is, and of course no one does. And I think bringing him along slowly in the role and monitoring him closely mitigates this risk. But the very real and possibly, potentially great risk is there.