I would say:
The Cpl is your commercial license for flying guess what "commercially" which means you can earn cash however it does not enable you to fly for an airline in the general case.
The instrument rating is generally required for most commercial operations i.e route flying and commercial procedures however the likes of banner towing, sight seeing etc are commercial operations but not needing an IR but its advisable.
The ATPL is required by the airlines to fly for different airline companies.
Confused yet.....