Though I left the JWs 35 years ago, I doubt that things in the local congregations have improved much since then. But when I was Service Overseer, I noted that in our congregation of 95 publishers, only 10% were turning in 10 or more hours per month. 20% were reporting 5 to 9 hours each month. 70% were reporting 1 to 4 hours.
The hardcore 10% were actually reporting 60% of the congregations hours. Of the 12 teens in the congregation, 10 were just putting in an hour or two until they were able to leave home and leave the religion. So if this is typical of JW congregations today, I'd say that of the 8 million JWs reported by the Watchtower, less than one million are hardcore. Five million are just coasting, and of that 5 mil, over 800,000 are just putting in time until they can leave home and leave the JWs.
Again my observations are based on my experiences serving as an elder in the 1980s. Perhaps things are different in the Borg these days.