I find it terribly difficult to gauge how many JWs truly believe it.
It's almost impossible. The organization has transitioned into situation where the entire organization is now a "Mixture" of PIMOs, PIMIs, and PIMQs.
Headquarters can't even figure out who is leaking out all the secret information into the hands of apostates like Loyd Evans.
The only thing that gives them away is their surface observable loyalty. Elders that hunt down the rule breakers = True Believers.
Those trying to fade = PIMOs