No, I wouldn't say the "fall" is "vague." Revelations is quite specific - the collapse of the business of churches,
(ie merchants wailing) The loss of its political power. The end of its idolatry. The take over of the churches by
people the bible saw as evil (I think of the various forms of Marxist theology and social activists who see the
church as a political vehicle.) And it won't be a place to get married in anymore.
Paul, amongst others, speaks explicitly of what would become of people's moral standings in the future. That
first church was under no illusion, despite the growth, that the church of the latter days would be huge, powerful,
corrupt and doomed.
This is interesting because
1 - the modern church would be unrecognizable to the New Testament (NT) writers
2 - the NT church was home based, small and growing and rejected the things embraced by modern churches.
Sure, some churches are still quite strong in America and the "third world" but the collapse has been going on
now since about 1900 - the attendance graphs are quite stark. Historically this is quite fast.