There’s a bit of a lore void here. Chronicles says that the Dalaran population was evacuated, and it’s clear that by the time Garithos is in command of the remaining Alliance forces there just doesn’t seem to be ANY Kirin Tor oversight.
IMO the most logical explanation is that the Kirin Tor was wherever the rest of the citizenry was stocked and had a very hands off approach to reclaiming Dalaran.
Of course I think this is a result of retconning Dalaran’s utter destruction in War3 to the “actually most people got evacuated” scenario we got presented in WoTLK, but the most logical answer is that the Kirin wasn’t active during Garithios command of Lordaeron.
Whether the answer is cowardice, fear or just focusing on taking care of the citizenry is anyone’s guess, but it’s made clear that the Kirin Tor just didn’t seem to be active during the time in Lordaeron.