Hasn't Tor failed to meet its goal so far? With only 900 exit nodes, it's totally feasible to block them all, which is exactly what China has done. If Tor isn't usable for hopping over the GFW, it hasn't yet fulfilled its true potential, has it?
People sure seem to believe that getting around censorship is one of the main goals, though.
Tor's user numbers in China in particular are very low simply because it's just straight blocked. Private bridges and pluggable transports can get around that, but they're just not used at scale because that's just too challenging for ordinary users.
The problem is more like that tor relies on a few directory authorities and the only protection they have is geographic distribution and the public outcry should a set of nation state go actually seize them.
Seizing the DirAuth wouldn't achieve anything useful: all the data that the DirAuth has access to is a matter of public record (literally, the role of the DirAuth is to collect that data, sign it cryptographically and vote on it).
A group of nation-states looking to attack Tor this way would need to stealthily subvert a majority of the DirAuth, and manipulate the network consensus in a way that is both hard to detect and allows them to deanonymise users; that's very far from trivial.
The question is whether someone would want to subvert or rather just shut down the tor network.
Yes, a simultaneous seizure of the DirAuth would do that, breaking Tor relays and clients until the software is updated (the list is in src/or/config.c if you are curious).
On the other hand, it's a move that would require international cooperation <i>and</i> cost lots of political capital, whose only result would be a temporary (but global) DoS.