Yep, it's viable for a short amount of time for single jump or single solar system trade runs. That's a tiny fraction of trade gameplay. That is exactly why it makes most sense to get rid of the T6/T7/T9 asap. The multipurpose ships are stronger, more secure, have more jump range, etc AND they do every kind of trading. The fact that you can do anything faster and safer trumps the tiny amount of cargo advantage the T9 has.How is the T9 not a viable choice for trading? (...) For a short A-B-A route (...)
You wouldn't be content with a fighter that can only damage one type of ship well or an explorer that can only scan one type of star quickly. Why are you content with a trader that can only do one type of trade run efficiently?