Once the Russian response did kick in, it overwhelmed the Georgians. But, once more, as Russian planners point out, a more numerous or experienced opponent could have defeated the Russians, and all the Russian flaws would have become obvious immediately.
The 20,000 Russian ground forces, including a single motor rifle division (which should be about 12,000) and the balance irregular local militias,were part of a very good plan that suckered the Georgians into being seen shooting first. The Russians massed and overwhelmed the ill-prepared Georgian ground forces with a rapid advance. Even so, the Russians lost a lot of troops for the few committed and the short duration of the war.
The Russian air force demonstrated severe shortcomings in proficiency, and only weight of numbers at the point of attack allowed them to pound the Georgian ground forces and make them incapable of putting up serious resistance.
The Russians are lucky the Georgians were trained as peacekeepers and not as combat soldiers, and that the Georgians lacked adequate anti-tank and anti-aircraft weapons. Russia may have fought their war relatively poorly, but Russia fought a war and Georgia did not.