I have run a niche forum for a few specific models of Mercedes-Benz, for the past 10 years. Right now I've got about 8,700+ members, with about 1,500 of them being active. My forum's focus in strongly on technical information -- HOW-TO tutorials on maintenance, repair and restoration, technical specs and information unavailable anywhere else (even from Mercedes-Benz), and basically providing owners with the resources they need to keep their cars on the road. I have about 15-20 members who are real experts and contribute amazing information for the benefit of the members, and have for many years.
Facebook has a couple of "Groups" that specifically cater to the Benz models that my XF forum covers. A few of my members are members of the Facebook group. They report to me that the signal to noise ratio in Facebook groups is extremely high .... meaning the value is pretty low in terms of quality of information. Basically I'm told (I have not had a Facebook account since early 2013) that it's a big show-off social club and tends to be younger folk who are not really that interested in repairing and maintaining their cars. The Facebook groups tend to be geared around posting photographs, want ads, and commenting on others' posts.
So in my book, not very substantive, because any sort of structure and ability to organize information is lacking. It's the on-line equivalent of a "Cars and Coffee" gathering on a Sunday morning at a shopping mall. Which is great -- there is a need and demand for that. But that sort of thing is very different than what a forum can offer. Although I have to say I recently did a member-submitted photo display with
@AndyB's "Photo Contest" add-on, and it was a HUGE hit.
Bottom line, I don't consider Facebook in the least as any sort of threat that siphons off my members. People who need real, substantive, credible information find me via Google; XenForo's SEO capabilities have if anything increased/improved that. People who want to show off and talk to others on a more "social" basis, go to the Facebook. There's room for everyone, and every type of venue.
The best thing any forum owner can do is focus on making the CONTENT of their site as relevant, informative and useful as possible to their members, and the membership will grow.
Cheers,
Gerry
P.S. I used Tapatalk on my vB forum for a number of years, and kept it after migrating to XF in March, 2019. And I kept it for about a month after migrating, when I realized that the mobile capabilities of XF were plenty fine for mobile users. Removed Tapatalk after letting my members know, and though a couple of folks were not happy, haven't heard a peep about it since, and it's nice to get rid of that (what I consider to be) insecure virus !!!