The last time we reviewed the Atlassian Cloud hosted products, they did not meet our security needs (requirements include isolated tenant from other customers, customer managed keys, etc) though they were much closer than a few years earlier. We also review the general security practices of the company (for example to make sure they implement a secure SDLC and follow other security best-practices).
Example: If you are a semiconductor manufacturer, you probably are not going to be storing all the documentation about your bleeding edge fabs on a cloud provider.
In short, that’s not happening for a wiki.
XWiki?
Well first its interface, if a non technical user can't user the tool that's going to be a big problem. Confluence has not the best interface but still better than Xwiki. The best the interface the better the adoption as a whole in the company. And for knowledge sharing adoption is critical. That's actually why Notion has been such a success recently. Even though their product is average, people want to use it, because they like the interface.
I don't have the time to do a full comparaison of other features, but wiki tools are in usage very different than collaboration tools. Can you have the list of last consulted documents ? Can you embed external documents ? ... Kind of the same things as Slack vs IRC
That should be your first prio before anyone locks one's information into your system...XWiki can import and export confluence and even wikimedia data, i never use a system when in cant import/export to the the next best product.
Are you drunk? Who tf ever wants that?