I think the difficulty here is that the JW use any scripture that seems to support their case to maximize output....Ofcourse synagoge has much to go with sunagogai ... the gathering of ourselfs together.
When you compare sunagogai the epi sunagogai one really has to wonder what epi sunagogai is. A normal religious gathering where Jesus would be in their midst was 2 or 3 in his name. That was a sunagogai. But epi? What could the wirter of Hebrew have meant. The other mentioning of epi sunagogai in the NT is when the christians meetup with Christ in heaven. I guess this qualifies for a christian to be the EPI-sunagogai of all times. The top most important gathering.
But Hebrew is talking about a practice in light of the end being very near ..... hmmm.... it sound as if these guys were gathering on a mountain in white robes to be carried away to heaven or something and criticized others for not going along in this foolish game.
However, I guess the question might be posed: what would a current JW perceive as the most important meeting? Certainly the WAtchtower study would not come into view. I guess most of them will probably say: the memorial/ last supper. And so ... by default you win with your hands down ....
But that does not mean they will not maintain you MUST be on the meetings in order to saved .....