It's 10, not 9. And there are severe problems with having a total of 10 DA be the essential source of truth for whole network. It would be trivial to DDoS the DAs and bring down the Tor network or at the very least, disrupt it: https://arxiv.org/abs/2509.10755.

It's the only complaint I have of the current state of Tor. Anyone should be able to run directory authority, regardless if you trust the operator or not (same as normal relays).