Your CPL holder has probably peaked academically, in terms of knowing about lots of "stuff", at the point they have taken their exams..and these exams are not pitched at degree level.
They'll move on to becoming a more experienced pilot by the time they reach 2500 hours but I'd hazard a guess whilst their hand/eye skills may have got better and they'll have a grasp of the specific knowledge needed for day today line operation their knowledge across the whole range of ATPL subjects will have decayed.
2500 hours of flying doesn't make you better at reading a sigmet chart or understanding why on a particular day the trop. over Siberia is below 20,000 feet than the CPL candidate going into their met exam..if they've gone to an organisation that used computerised performance data I'd hazard a guess the 2500 hour pilot may well have forgotten some of the little performance gems and wrinkles that they needed to be aware of when walking into the exam hall.
Nothing wrong with any of that, they should be better equipped to do the job after 2500 hours, but that is what makes (IMHO) the ATPL a vocational qualification, not a degree.