Yes I find myself thinking similar thoughts. The growth of JWs during the 20th century was pretty impressive, despite those who like to downplay it, yet the communities they have established are ultimately pretty weak and prone to decline just as fast, or faster than they appeared.
I compare it to the decline of the Church of Scotland which has been on a downward trend for over half a century. Some have predicted it will close before 2040. Yet in some ways it displays more resilience than JWs. Ten years ago I would never have expected that the Church of Scotland Yearbook would outlast the JW Yearbook, and yet here in 2019 the JW Yearbook is discontinued, and the CofS red Yearbooks are still going strong.