It sounds like you don’t understand what is claimed.
There is an often repeated claim that while the best AI has beaten the best human chess player, a combined human/AI player beats the purely AI player. The idea is that an AI and a human collaborating together will play better chess than just the AI alone. This arangement (an AI and a human collaborating together to play as one) is often called a “centaur”. Akin to the mythical horse/human hybrids.
The sentence you asked about, the “Now the best chess AI are only held back by humans” claims that these “centaurs” are no longer better players than the AI alone. That the addition of a human who is meddling with the thinking or the decision making of the AI makes the AI plays worse chess than if the human would be not present.
Sure, humans built the systems and they are interested in the results. Yes it is a human endeavour. That is not what the claim disagrees with. It disagrees that a human meddling with the AI mid-game can improve on the outcomes.
