I've been told that using hypothetical case studies is normally "too perfect to be true" especially when you are using that one business all the way throughout your essay, it really comes through. Experienced HSC markers should be able to differentiate easily between real and made up businesses and they would definitely prefer the first.
When the business is made up you tend to make build it per according to what you're trying to say/prove and it generally ends up without any flaws and I suppose limits your response to being really one dimensional. A good essay should really show why the business is doing well and why it isn't, meaning ways of improvement (strategies) are necessary and thus you need show where it failed. With hypothetical ones they generally lack in that aspect?
Having said that it is still possible to achieve B6 with a fictional business. Although real life cases are preferred it is not compulsory. If you really want to use a hypothetical business I recommend having a real business for the one that can link to all the syllabus dot points (so a big general one, maybe the one with the most resources available out there?) and for other really specific examples where another business example might work so much more better, use a hypothetical one.
Please correct me if I'm wrong.