Smaller Courageous conversions bought more flight decks

Did the lower tonnage of Courageous-class carriers offer any advantage over Lexington, Akagi, and Kaga?

Yes: it conserved treaty tonnage and allowed more carrier hulls, though it did not make each ship individually better.

The Courageous-class ships' lower displacement was not empty capacity that could simply be filled with another eleven thousand tons of equipment. Adding that much weight would require major structural, machinery, and internal-volume changes. Their real advantage appears at the fleet level rather than inside each hull. Using less treaty tonnage allowed Britain to maintain more separate carriers, creating more flight decks and more opportunities to distribute aviation across theaters.