Light aircraft flying will build stick and rudder skills, pilots will learn decision making, and the inevitable errors won't involve involve an airliner with 180 pax at a major airport.
A new CPL holder has had to cram in and regurgitate all the knowledge for his license exams, type rating and company SOPs, of which only a certain percentage has been fully retained. The necessary things are found out in the real world. In the 30+ years of flying since I did my CPL I can honestly say that I never used my knowledge of hard and soft iron magnetism or Mercator's projection.
Give me an F/O with even 500 hours total and a couple of hundred of those in the right seat of a turbo prop, over a new MPL graduate anyday. 200hour pilots are fine as second officers where errors aren't critical and they can watch and learn.
Unfortunately it is difficult for airlines without a long haul fleet, that are in countries without a large military or general aviation pool, to find suitable applicants.