Gat vs. revolver: Gats are heavier and because of their high rate of fire, need a large ammo store with a high-rate feed system, which makes the whole installation much heavier and bulkier.
The Russian approach in the Su-27 has been to reduce the number of rounds and burst length (because flight control and sensors and HUD make the shot more accurate) and stick to a single-barrel gun - which is not even a revolver cannon:
DEVELOPMENT OF SU