It could actually have been a lot worse than nothing. Compare covid deaths in Japan and Korea prior to the mRNA vaccine rollout in 2021 to afterwards; afterwards the infection and death rates sky-rocketed.
Sinovac was something terrible like 50-62% efficacy. While also not provably stopping transmission. The spread would have continued and there was no evidence it would have reduced the burden on hospitals. It would definitely be worse for people.
The reason PRC never said it publicly is because that would have been terrible for them politically as well.