It's all a matter of perception. To me, it was a victory in 3 ways, the Army of the Cumberland managed to reach Chattanooga and weren't pursued by Bragg. In this state they were broken and Bragg could have captured thousands of stragglers and take them prisoner and cut Rosecran's Army down.
Second, the Union inflicted more casualties on the Confederates-losses they couldn't recover as easily, including 3 brigadier generals dead.
It forced Bragg to lay siege to Chattanooga, something his army wasn't prepared to do. When the Confederates lost their positions on Missionary Ridge, the Union discovered that their besiegers were suffering from the cold with a lack of proper clothing and scantly rations. The siege, though nearly successful is starving the Union to surrender, also left Bragg vulnerable with an ill led and equipped army.