Russia has never achieved air superiority in Ukraine.
Additional Ukrainian AA capability via Gepards will make the Ukrainian airspace even more dangerous for Poccners, which will greatly limit their capacity for defense operations.
The Black Sea is now extremely dangerous for Russian ships and they have pulled back very far from the Ukrainian coast. The same will happen to the skies.
No single weapon is a game changer. But it's not going to tip the scales in Russia's favour. Quite the opposite.