CR is still pretty much militant, as there is constant need for them to be, they possess a good few battleships and I don't really know about any other enemies of them being as hostile as Outcasts are. Council enjoys the secrecy of Roussillon, neither GRN nor the outcasts know where it is despite the constant guerrilla presence of Council forces in the Tau sector. For a short period of time, we can divert a few battleships too into the neighboring systems at any time. And as you earlier said, Outcasts have quite many enemies within whole Sirius, I don't think they would risk weakening on an existing frontier just to open up a new. Who knows when would the Corsairs strike, just to mention an example...
If we think about who could beat who, we better consider the odds a bit more realistically, don't you think?