THe 'little 4' were always utilized poorly anyway.
The tholian Web takes place over just a few hours, but in order to get a few more lines for Uhura--inexplicably in the middle of the crisis she goes off duty, changes clothes, sees Kirk's apparition in her quarters, gets sent to sickbay, is declared sane, goes back to her quarters gets changed back into uniform and goes back on duty it time for the climax.
In 'Elaan....' Elaan uses Uhura's quarters---clearly just to get a couple of lines throw in for her. What, they don't have a few nice guest quarters?
The only time they used Sulu & Uhura right was the first season when they were off duty and or asserting themselves on the bridge.
In 'Man Trap' Uhura really gives it to Spock when he glosses over a landing party death. When did she ever speak her mind after that. Did they get mail that she was being to 'uppity'?
In Balance...' Sulu goes along with Styles and pushes Kirk to put the ship on intruder alert. I can't think of another time where Kirk or Spock didn't shoot down any advice or comment by Sulu.