I think the article was generally reasonable in its assessment of religious belief/practice in Britain. But the journo who wrote it confused the regular knocking on the front door by a JW with "fervour".
JW's do not exhibit fervour, unless it is 3 Elders DFing a perceived Apostate.
Nor do JW's fit this description "People who are religious in a counter-cultural way know what they believe, and could argue it out with people who disagree."
JW's cannot explain what they do believe, let alone defend it.
For these reasons the JW's in Britain are as much an anachronism that will fade away as is the Church of England itself, for different reasons.