However, full to the gunwales is full to the gunwales regardless of who is providing oversight? No?
No .
Full to the gunwahales for Airline A may be different to Airline B.
The performance engineers can do all sorts of fancy things behind the OPT scenes that most, including the line pilots, have no idea about. For example, they might shorten a runway by several hundred meters thus resulting in higher thrust settings than the regs would require, without any visibility of this to the crew. Airline A might do this and Airline B might not.