I hear you. After thinking about it a lot for ages, and after seeing that documentary, I've decided the problem was Tony Banks. I Can't Dance is his fault. The singers are red herrings since both of them are on some of the bands best recordings.
While Invisible Touch was still better than %99 of the albums released that year, that's not much consolation when you think of how many 70s bands are still making great stuff. Maiden's Empire of the Clouds, for example, just last year. Genesis could be doing that now and isn't and it's kinda sad.