This discussion is really interesting, thank you :)
I think we'll have to agree to disagree on the nature of potential/expectation/and so on. I suspect there's a difference if you know baseball and how it works to if you don't, as I'm not looking at it technically from what the role of the Ace is so much as the characters and the way they speak and interact. I do agree that they also have faith in Furuya but I still feel that the putting him in in the Yakushi game was a valid decision based on psychology against Yakushi and it might not have happened against a different side. Raichi was fourth up to bat, all it would have taken was one mistake for Raichi to be at bat again, and then the whole situation changes, so it didn't seem silly to me with Miyuki injured to bring in Furuya, as Kataoka is fond of taking risks. He brings in Sawamura too often in earlier games for me to see it as them not seeing any potential for him to be the ace. The similarities between Sawamura and Kataoka are why I feel that's always there in the back of his mind.
Kataoka says he's not going to sacrifice the team for Furuya. If Furuya was the ace in the way Ochiai sees him, then that approach might be different. Kataoka's main focus is the team, and the win, and that for me inspires the other decisions he makes, some of which are psychological for his team/the opposition, and some not. But we can agree to disagree. I think it doesn't matter overall as it ultimately gets to the same point.
Miyuki's weakness as a character is that he thinks and calculates too much. If you look at his batting, he aims for the hard shots but sometimes spoons the easy ones. He's always looking for a way to run a play to take down the opposition and he calls aggressively, which can be good but is sometimes without realising the state of mind of the pitcher on the mound. I have never thought that he doesn't recognise either Furuya or Sawamura (or even, on his day, Kawakami) as the ace, because for me Miyuki sees as the ace the pitcher who is performing to his calls and getting the strikes/outs on the day and in that match. He's not at any point demonstrated for me a sense of being preferential to one over another, he's happier to play them off against each other to keep them on their toes and thus performing, even while not always realising that isn't the most positive outcome for the pitcher, confidence wise. His ability to do that makes him flexible between pitchers and that works well for the team overall - if he were to be too wedded to the idea of one ace, it wouldn't benefit anyone, so to do it seems out of character. He's capable of assuming x pitcher is more on form and thus more ace-teki than the other at one point or another - but he really isn't faithful in his approach to one over the other, at least to the point I'm caught up. And since all the Sawamura-accepting stuff apparently happens after that point, I'm probably not going to change my mind. There's nothing he says that I can bring to mind that suggests he is really playing favourites with one over the other. They're all...as he puts it...kono team no daiji na senryoku...important battle components in this team. He also uses the same term to refer to himself after the Yakushi game when the coach apologises for keeping him in, saying that if the coach saw him still as 'senryoku' then that was fine. That's where Miyuki's motivation is in my opinion.
Miyuki's main character development points come from his weaknesses, too, so I feel like whenever he doesn't do something that ultimately benefits the team or when his judgement is slightly awry, it's building him as a player as much as it is the aces.
This is the view of someone not au fait with baseball as a game overall and who has mostly learned anything about the game from this series, so there may be real life technical decisions that I;m not aware of. But I'm not really interested in them, as this is a fiction and more about the characters. Again, I'm happy to agree to disagree - I am just not personally persuaded that the key figures haven't seen Sawamura as a potential ace much earlier on in proceedings than they are generally given credit for.
Also, as another disclaimer, I don't have a personal preference for Eijun or Furuya and really don't get involved in those debates (XD). So it doesn't matter to me who is seen as an ace by whom at what point - it just seems to me that the expectation is there a lot earlier for Eijun than some people give credit.