Thanks for your investigations!
In general, as @micmc pointed out, there is no real benefit of multi-tenant setup on Cloudron.
The biggest benefit I see is a clean dashboard. I did such a setup on other hosting platforms and never had trouble with that.
While an app can have multiple databases on Cloudron, we have to investigate if it's worth the trouble of supporting such a setup.
Yes, I'm wondering this request is so rare.