I wouldn't necessarily include business in fluency, because obviously there's so much technical jargon for any industry. I agree general polite forms and grammar carry across, but I wouldn't expect someone to be able to speak hospital talk or stock broker talk etc. I'm sure I know what you mean, being able to work in a real workplace setting, just wanted to be more granular.
Also, for dialects, there are plenty of natives who cannot understand dialects of other natives. Would you call them not fluent? That's something literally everyone has to learn from experience.
For me fluency is really about commanding situations that any adult could in their native culture. Negotiate a car payment, open a utility account, get your boat license, partake in a political process, apply to a vocational school, find the right school for your child, read the fine print, pretend you understand the fine print, discuss miniscule details of a tv show, explain to the doctor why you think you have cancer, know how to act at a funeral. I realize there are a lot of adults who cant even do these things in their native cultures. Half of GAF admitted to not knowing how tax brackets worked. Stupidity in the general population is understood. I would just expect the same level of basic stupidity in another country NOT BECAUSE OF LANGUAGE BUT BECAUSE OF EXPERIENCE before you call yourself fluent.
If that makes sense. Being able to carry a convo about your boring weekend without pausing and correctly aizuching does not make someone fluent in a language.