It's good enough not because people will stop at that, it's good enough because the Great Firewall is one piece in the overall apparatus that "repression" is. People who go beyond the limit will emit other signals that will be caught: they will use non-chinese censorship-resistant softwares, they will connect to non-chinese ips, they will have a secret life that appears suspect to their friends and family, they will raise controversial topics while at work... much like OpSec, running against this system requires impeccable hygiene that will be caught at some point or another.
The Great Firewall will be enough for most people to not look for trouble, but they need the other means to make sure curious people are kept in check