I really don't know because like I said, hitting a lot of balls has yet to mean anything to the story. You still only play with one lol. For example, nowhere does it suggest Tezuka can hit more than one ball, yet he has PoP. Because Tezuka's tier is absurdly high, I believe he could beat Kazuya without having to hit 10 balls, which destroys the whole argument of "more balls = better player." So really, I think Konomi just tried to add something stupid to the story that he is finding out doesn't actually work in the end.
Is just a way to show a players skills, but in terms of strength, it doesn't matter that a player can hit 10 balls or the balls he wants, players who hit less balls can win.
For example, Sanada. We know he can hit 5 balls at the same time, but he would destroy most players of the G10. It doesn't matter, in the case of Shuuji, he is a player who can hit 10 balls for sure, so what? He can lose to players like Yukimura or Sanada, rank doesn't matter, the overall strength is what matters.
I believe Tezuka, would beat Oni, Irie, Kazuya, Duke... it's not assumption, he is ithe top of the MS, his base stats are strong plus he has Hyakuren, Saiki and POP. So there are people who say, Oh, POP it's nothing to the top of the first string, they'll be able to deal with it even if is Tezuka who's using it, wrong. It just depends on the player that's using it. Tezuka was really strong before activating it, with it, he can be the No.1 of the first string perfectly. Just the fact that he can't hit 10 balls doesn't prevent him from being the best, because after all, the number of balls you hit it doesn't matter, is the overall strength. Also, probably Konomi made him go to Germany because if he stayed in Japan, he probably would have become the No.1 in no time, really quick, so it was pointless that happened without giving other players any chances to do that and show their improvements.
Konomi just wants to say to us, "hey, these dudes can hit 10 balls, so watch out because they're really strong", but a player like Tezuka with POP who hitting 10 balls at the same time isn't a matter for him, it doesn't make a difference.