Some would simply call it an evolution of style, and others might call it a sellout. I'd like to hear your examples of musical acts that changed so radically over time that you'd consider it a sellout.
I started to type out a huge, involved comment, but I don’t want to come across like mirror-world Patrick Bateman, so I’ll just say here: Genesis. 1970-1976 and 1978-1998 were almost like two completely different bands.
I think it is fine to just treat them like two completely different bands. Personally, I like both of them. But if I had to pick one 70-76 of course would be the choice.
It's taken me years to regain an appreciation for their post-Duke catalog. I was intensely negative on anything later for close to 15 years. Slowly I've been able to rediscover what it was about their later output that I initially liked, and maturity has smoothed out some of my own rough edges as well. I still find We Can't Dance to be unbelievably limp and lifeless, though.
1978 marked the departure of Steve Hackett, probably their proggiest songwriter. There's still a bit of old Genesis magic in the following 2 records but by 1981 it was basically completely gone