I think Jimmie Walker as JJ Evans became the breakout character on Good Times even though the show spun off with Esther Rolle's character.
Also, on Alice, Flo quickly became a fan favorite with her big personality and "Kiss My Grits" catchphrase. However, I always felt Linda Lavin was a great anchor character for the show, so I never felt Flo overshadowed Alice.
I disagree that Niles stole the show from Frasier. Both he and Kelsey were a great comic duo and they needed each other like Laverne and Shirley or Lucy and Ethel. Kelsey made Frasier's journey to find long lasting happiness with a woman interesting and funny to watch. Grammer deserves all the accolades he's gotten from that show.
Of course, David Hyde Pierce was a revelation as Niles, but no, I never thought he stole attention from Kelsey. Similarly, I felt Mary Tyler Moore and Bob Newhart absolutely never lost the spotlight to their gifted casts of supporting players. It's just that all three stars were very generous with giving screen time to their costars.