Companies may employ a number of people in many of these roles. You could have 30+ animators on a project and a large company might be working on 3-6 projects at a time. And some of the positions are unique so there may only be one or a handful of people in that position at the company.
Note: Compositing is also used in 2D to 3D conversion. Although it uses many of the same tools and skills, it’s a different task, pipeline and different goals. Compositors can work on standard visual effects shots or conversion but will more likely need some initial guidance when switching from one to the other to learn the pipeline and additional tasks.
Companies should be clear of the type of compositing they are looking for and job seekers need to confirm what type of compositing they will be doing.
I've now seen a few job postings with Supervisor in the title (CG Supervisor, Production Supervisor, etc) and then discover that some of these are considered Coordinator level positions, even though the posting implies supervising people. I find this very confusing and it may be strictly to get these people classified as management to avoid paying overtime.
To be clear - a supervisor position is just that, supervising others in terms of assigning tasks, overseeing the work, guiding them, etc. They need to know the creative and technical aspects of the area they're covering and should know as much more or more than those they are supervising.
A coordinator typically is one who gathers and dispenses information at the request of a producer, supervisor or others. Their role is to help coordinate or sync different people and departments to make things run smoothly. They work with others but do not typically manage others (possible production assistants) And they should not be considered supervisors.