They are delusional because other people don't see what they see. So by the definition, they are delusional. Many people in the mental wards see things that others don't see.
These guys are not mentally ill though, they are practitioners of major religious institutions, they are church leaders and pastors etc. We are forcing God into a box by saying that God must do this or do that in order for us to believe.
How do you know? There are many people who have not been diagnosed yet. Many politicians, CEOs are psychopaths. Religious people who hear or see things that are not real are mentally sick. Anyone who hears or sees things that are not real (Jesus or Muhammad riding on buraq are good examples) is insane.
Sometimes your mental illness will still allow you to function in today's society without causing too much harm to yourself or others. There are of course the Jesus camps for kids etc. which cause some real and life lasting harm.
Look up the definitions before you proclaim your truths.
There is nothing to debate. We all share the same reality, and if someone perceives this reality differently, well, they are either geniuses or delusional.
In the future, religious beliefs will be classified as mental delusions. It is a matter of time. Science will march forward and push the Bronze Age myths to the footprints of history.
Once the church will lose its political power, the con will be over.