So the distinction could be “marketable” vs “profitable”?
We found that Product X was not a commercial proposition
We found that Product X was not a viable commercial proposition, or
We found that Product X was not a commercially viable proposition
A geography teacher at school used to excise the “viable” in our essays which prompted this post. It still smacks of jargon to me though I agree with what you said. Viable sounds like a popular-economics buzzword uninformed schoolkids use when trying to impress (raises hand!). Best to avoid the word entirely, perhaps.