A Galactic Empire fleet in the Space Battleship Yamato setting

How would a Galactic Empire sector fleet after Yavin fare against forces in Space Battleship Yamato 2199?

It could exploit opponents who were initially disorganized, but the panel expects serious difficulty against organized formations of comparable size and weapons such as wave-motion guns.

The proposed advantage for the Imperial fleet is its organization when it first encounters an unfamiliar setting. That could help against opponents caught unprepared. The answer becomes much less favorable once similarly sized enemy formations are organized and able to use their own weapons effectively. Wave-motion guns and the imagined need for extraordinary defenses make this a comparison of fictional capabilities rather than a prediction about real naval combat.