My favorite scene in BW is when the gym leaders all show up and fight the sages.
It was very disappointing to see the Gym Leaders go back to not do anything at all in XY after Gen 5 really excelled at giving them presence. Other than Korrina, I think the only Gym Leaders outside Gen 5 to actually do anything in the story were Giovanni, Jasmine, Clair, Norman, and Wallace (and Wattson if you include New Mauville). And Clair's role was to delay you getting a badge because she was too full of herself to admit she lost.