So you're positing that it's in a significant % of cases possible to fly business at less cost than economy? If so, you'll need to back it up, because it's a very bold claim to make.
full fare economy will mean fully refundable and changeable with no fees etc. discounted business/first class will be just like discounted economy - not refundable, and not changeable w/o fees - the latter can definitely be cheaper if you don't mind the constraints.