In short, his main criticism is that WikiTree generates a genealogical "pensée unique". A thought reinforced by the very Frenchie defiance against America forcing the entire world to be American (a sentiment not totally baseless, if you ask me).
First, I would recommend that you not refer to any French citizen or francophone as a "Frenchie", as that is sometimes considered derogatory.
Second, forgive me as I'm going to address a bit more than what I've been asked to by your question because I would agree in part with your detractor friend and his critiques.
So I'm going to offer what may be an alternative view here: WikiTree presents both pros and cons for a genealogist like your friend.
Part of the problem with how this question is being presented, is that it's an either-or scenario. I mean, I don't do all of my genealogy on WikiTree; do you? Sometimes for DNA stuff, I'm dealing with living people and I'm not about to put that info on WikiTree. WikiTree is my place for documenting the dead and possibly connecting to living cousins with their willing participation.
Moreover, as you present it, there's only one type of genealogy. I'd say that there's at least 3 kinds:
- Standard Genealogy (quotidian, straight-forward)
- Difficult Genealogy (novel, publishable, sometimes speculative)
- Disinformation and Misinformation Genealogy
There's a big difference between the novel, publishable stuff, and the quotidian stuff. If something were to be a publishable thing, a collaborative site probably isn't the place to do it. But if your friend has 280,000 profiles, surely that isn't the game unless he has a very large book in mind! If he does, great. Encourage him to get it written up and published!
It might also help you to consider WikiTree as being more analogous to Wikipedia: You do not and cannot publish original research in Wikipedia. Perhaps your friend views it as an inappropriate place to publish his work. He may not receive sufficient recognition or compensation (e.g. book royalties) for it.
To me his view is very analogous to the practice of science:
If there is debate, it's better to have each genealogist publish independently his/her view of things, than trying to reach an impossible consensus in a collaborative way, often resulting either in a "strong voice" imposing her version of things, or endless wars.
Lots of science is "settled" and verified as far as we as humans can go. That stuff can largely go in Wikipedia. But much more is unknown, and that stuff goes in peer-reviewed journals. Scientists spend our efforts on the unknown insofar as it is possible, plugging away at a problem, not emerging until we're ready to publish the solution. It isn't the only model, but it's the dominant one.
As part of that analogy, I'd note that scientists sometimes have that same problem that genealogists have with (Ancestry) user trees & hints have: disinformation and misinformation. Some myths are really stubborn. So it helps to publish definitive summaries of research and publicly accessible profiles of that research. Many genealogists do the same here and elsewhere (often out of frustration) due to false information being propagated user trees, hints, and even by ThruLines. It isn't that we lack a consensus; it's that the misinformation has taken over. Those who accept evidence-based conclusions have no trouble reaching consensus on those erroneous conclusions and correcting them.
That propagated error also represents a form of unhealthy ideological conformism, IMO. And WikiTree is probably the best cure because one can make a public case about what the truth about who your 5th great grandfather's 3rd wife really was.
But for the quotidian stuff, WikiTree has benefits and private trees can have drawbacks.
Time. Good genealogy takes time. So why reinvent the wheel? Collaboration takes some time and effort, but surely not as much as the duplication of effort spent verifying and re-entering all of this data does! How much more of his time could be spent on original genealogy work, with interesting questions, were it possible to avoid re-researching (in depth) everything that someone else has already done!
On the flip side, for time, joining WT has some massive start-up costs: Imagine the headache of uploading a 280k profile GEDCOM file!! That kind of stuff isn't advised, nor, IIRC, permitted. Even one's own smaller tree can take a long time, particularly if seeking to maintain a high standard. That too can present a problem for someone who does genealogy professionally: Everything on WT is public and one will undoubtedly stumble along the way. Are we comfortable with that? I don't know: I've certainly seen some in G2G publicly chastise the efforts of new users.
Interface. WikiTree's interface takes time to learn, but you need to consider that WT is a de facto Anglophone website at this point. No big steps have been taken toward regionalization. Geneanet, is based in France and available in French. That probably works better for a francophone.
Monetization and paywalls. Geneanet and WikiTree both are available for free, however Geneanet, like Ancestry, charges for some stuff. Both Geneanet and Ancestry place "public" user-created family trees (which are not restricted as private) behind a paywall. Consequently, others only get to find and see your tree if they pay first for the privilege. Here on WikiTree that is not the case. Yes, the site is still monetized - every site needs to earn money to operate! But WT does not put up a paywall. I want others to find my research. I want the research to survive my future demise AND stay free and open.
My general observation is that few are convinced that WikiTree is the ideal choice right from the start; instead, users tend to fall in love with it.
Be sincere, and just invite him to give WikiTree a test run. Just to get himself connected, then no pressure. Don't enter with any burden of expecting any results. I would re-iterate to him that you are NOT asking him to add is 280k profiles here. Offer to be available and take initiative as a mentor for him, to make everything as easy as possible; in fact, you should see if you can build out a branch on WikiTree that will ensure that he's connected from day 1. (This is why a week ago, I made a feature request so those we invite to WikiTree could be connected in a simpler, faster, streamlined manner.)
Maybe he will fall in love with WikiTree too.