You are underestimating, by a mile, the editorial effort that goes into fighting scam and spam, vandalism and lies. Wikipedia does have a support structure to do that, I doubt instance admins have the same kind of resources.
Also, any such wiki has to be allow-list only by default. Any open wiki is vandalized with spam and hate speech almost immediately. Open federation would make this trivial.
That structure is extremely corrupted though. And Lemmy shows that volunteers can handle this kind of stuff. Though Ibis will definitely need a lot of mod tools.
Of course no single site is perfect. Editors may always have ulterior motives. That is what the editing history is for. But with a federated wiki, the only thing you'll get is multiple different versions that all present their oen little "truths" and at that point you can just go back and search the entire internet for blogs, just like the website you sent me is a blog.
I think thats better than having our single "truth" controlled by a corrupt organization from a different country, different language and different culture. With federation there can be independent wikis for my local country or city.