I don't think it would be fair to blame Collins alone for Genesis' blandification, but somebody needs to be called out (maybe the whole band?). Sure, Peter Gabriel was a loss, but other bands lost significant players and still continued to produce interesting music (e.g. Soft Machine without Robert Wyatt or Kevin Ayers, Gong without Daevid Allen, The Velvet Underground without John Cale, the Byrds without Gene Clark or David Cosby, and probably lots more with whose history I'm not familiar).

In my perspective, the problem with artists like Phil Collins isn't that they're not good enough, but that they garner listeners who might have otherwise sought out more challenging performers.