I believe the rating doesnt determine whether you are captain or not, I believe it is firstly down to the licence you hold, (ATPL or CPL) and then your company internal requirements and assessments.
For example as I said at our company, everyone does the same type rating (as there is only one type available), and then the company determine who is a captain.
You can have to pilots flying together, with exactly the same rating, both with ATPL licence, one pilot with 3000 hours has passed the command assessment etc, the other could have 10,000 hours but not passed the command assessment and is not a captain, even if he was a captain at his previous company.