Well, I could only imagine that this so, because a differences course for the classic for Vision-only Pilots does not exist atm. If Bombardier or CAE would offer an approved classic differences course, this is what you should be doing and not an initial type rating. I am sure that they would offer this, if enough demand for this should arise in the future - as long as classic versions of the AC are flown, this will possibly be the case.
Maybe all this is a good reason NOT to progress to the Vision, as sooner or later there might be more demand on the classic again. Rather wait and move on to the 7000, because it is a different type.
One other thing I have noticed, is that many staffers don't even have a clue about all this and many understand the Vision being a completly seperate type rating and treat it as such, which it certainly is not. After not even 3 years, it has become quite rare to get a job offered on the Vision without having any actual practical experience with it.... even with thousands of hours on the classic.