As @jomaxro already quoted, the support statement is right there in the howto for subfolder. I don’t think it needs to be hidden, it’s there for any hosted enterprise customers or sites willing to accept the likelihood for complications, which you did when you read the document and continued down that path with your install.
All your experience has really done is prove that point. The team are very honest about what Discourse can and can’t do, all of the recommendations are there to give would-be administrators and developers a chance to enjoy and succeed with the product.
For those who choose to go off the beaten track the odd ‘thar be dragons’ sign is erected. The thing about dragons is that for the right price someone is usually willing to assume the time and risk to come kill them.