That's not the picture the fiction we have of Caleb-era High Command meetings paint. He's oblivious to any possible threat outside of some nebulous Capellan plots. All the competent HC officers depicted are freaked out by the DC saber-rattling and doing everything they can to go around the Prince and reinforce the Sandovals, who are up front that they don't have the troops to combat the threat they're facing. Yes, it's their job to manage that border, but part of that is realizing when your 1/4 of FedSuns strength isn't enough to ward off the concentrated might of the DCMS and mercenary support.
Really, it reminds me of nothing so much as the 1st War, where the AFFS was judge the Confederation their more dangerous foe and were preparing a spoiling attack against the CC and got blindsided by Minoru Kurita's offensive. The difference is that there the whole High Command miscalculated and were shocked, whereas here we see multiple Marshals trying to talk the Prince out of attacking Capellan phantoms no one sees but him, and working behind his back to mitigate the DC attack they all see coming.