The BeeGees - they became disco boys at the time of Saturday Night Fever, disgusting. 
Genesis - Beginning at 'Then there were three" Phil Collins ruined that band. 
They proved they could still produce with Trick of the Tail minus Gabriel, but soon after it began to slide down the tube.
Supertramp, Beginning at “Breakfast in America” - Sad sad sad…
The Doobie Brothers - once Michael MacDonald became the lead singer. Rock went Pop. 
