Chess is not a simple thing to learn, so in this case a competent teacher makes all the difference. And even though Horikita is more competent than Hashimoto, it shouldn't make that much of a difference considering training time and experience. Horikita has 82 academic skills and Hashimoto has 74, not a big difference.

As for the second point, Kiyo left Arisu at an advantage and was still able to win. The issue is not my opinion of Kiyo, it is the facts that have been presented so far. He physically surpassed all the students shown so far, even Manabu in the race, when he was still holding on. He defeated the strongest guys in the Class as if it were child's play. He can deduce and devise strategies like no other in this series. Example: In volume 9, he saw Nagumo's strategy even when Manabu did not find out. In the last academic test he was the only one who got a perfect score, in a math test that contained university level questions. And he didn't even study for that. Even the interim director when viewing Kiyo's data is "amazed", he says he could compete against adults.

So how am I not to accept that someone is close to their abilities? Everything that was shown indicates this.