The number of qualified PPL's that I fly with who are unable to maintain heading or hold altitude to within tolerance for the PPL let alone the CPL is somewhat disconcerting.
The tolerances for the CPL are more limiting than those for the PPL.
To say that you will not learn anything on the CPL course is very presumptuous; for one thing, we ALL learn and when practising we all (well, most of us) improve, whatever course we do, even refreshers and you may just find that you're not as good as you think you are - not YOU personally, just generally speaking.
With nigh on 600 hours, with Complex sign-off, Night, IMC and FI(A) Ratings before CPL(A) I can still honestly say I learned a lot on the CPL(A) course. Thank you On Track!