I'll speak from experience as a person responsible for official languages and language training in a crown corporation that is not subjected to the CBC levels. We had our own rating level.
What's important here is whether you can perform your job in both official languages. If I were hiring an IT person, my interview with this person would be strictly IT based. I would pretend I was a caller calling to get information from the help desk. I needed help with something. If the person couldn't answer in both official languages, then they were not at the proficiency level that we wanted. We want advanced level, not expert, which is equivalent, I believe, to the C level within the public service.
We're not asking for somebody....You know, I make mistakes when I speak English. I still do interviews in English, and people still understand me. It's the ability to be understood and to understand. I still say “air” instead of “hair”, but people understand when I speak, and that's what we're asking. That, I believe, requires the C proficiency level.
Should it be built in? If you think it's necessary, but at the very minimum we should say that they should be advanced in their own field of expertise. If we're looking for an auditor general, they should be able to explain processes and whatever in both official languages.