A very good source in the UK CAA once told me that British Airways had done a trial back in the late 80s early 90s where they had put a course of sponsored cadets through a B757 type rating before completing the CPL/IR in an effort to persuade the CAA that the light aircraft time was unnecessary. Their case was that the Cadets all passed the 1179/IR with no noticeable difference compared to the CPL/IR candidates.
The CAA were not persuaded.