So you are mischaracterizing the biologics then. They are indicated for UC in the US. It's just that the doctor thought that combined, higher doses would work better (and apparently it did).
The prednisone still had him shitting blood 20 times a day. Cheap indeed.
How do we even have a conversation if you take drugs that are approved for treating a condition and just hand wave that they are "not tested"?
Why not force society (via insurance premiums) to pay for some testing? It's not like combining drugs with different mechanisms is a stupid experiment.
The gold standard for testing the combination would be to test it against the standard of care, so it's fairly precious to complain that the doctor and patient here don't have a big enough pool.
Just one of the biologics is 500k/year