A very large part of those two albums being good was Steve Hackett (whose solo material I highly recommend). After W&W he departed and then Genesis became the pop trio that most people know
As I said in an earlier post, my reference was more about being the primary songwriter, or at least a very significant part of the band, since Czech's crack about Foreigner's drummer dying stopping the band just made me think of long-running industry jokes about the drummer being the most disposable band member, as the old joke goes: "Who's that guy who hangs out with the band? The drummer"