China is not bad at a science victory. They don't have any direct bonuses to science production except for the 10% eureka boost. This helps minimally but, his extra build charge helps alot more than this bonus. His extra build charges and the ability to boost wonders allows him to quickly gain integral wonders for science production such as The Pyramids or The Mausoleum at Halicarnassus. Another wonder to rush early for more great people could be The Oracle. Overall, with no direct bonuses to science but a few nice ones, this lands them at a 4/10 for the Science Victory.
China's domination rating is not actually based on how good at domination they are, because lets face it, they have only one bonus unit for combat and it is really underpar for attack, their rating is for how good they are at defending a Domination victory from the opposition. They have the Crouching Tiger, which as low range for a ranged unit, but does pack a punch for the medival era they are obtained in. This range weakness is solved however with China's primary tool for defense, The Great Wall improvement. This improvement is essentally a fort available in the Classical Era, and because of this, their early game defense is near impenetrable if played correctly. Overall, China is pretty good at defending against others, but on the offense they can suffer greatly due to no combat bonuses and the unique unit being kited, this lands them a 6/10 for defending against Domination Victory.
Culture is what China is made for, this is the victory type you should attempt 99% of games, they have a ton of useful tricks in their arsenal to skyrocket their culture in the early-mid game. They have the extra builder charge, which helps with early game development, and they can speed up wonders with their builders, which the culture victory heavily benefits from.