It's an old argument, and those with any real experience of cadets vs experienced FOs will all say the same thing - it makes little difference. It is more about training, aptitude and, above all, attitude. The US 1500 hours limit is a band aid for the FAA to appear to be doing something after a spate of regional airline crashes that were more due to fatigue (which they are also addressing to some extent) and lack lustre training and attitudes, which they are not. Look at the various runway over-runs, the landings on incorrect runways or even airports, the SWA wheel barrow at La Gaurdia... the list goes on, but none of those accidents had a cadet FO. But do we see an unduly high accident rate in Europe, where cadet FOs are the norm, and have been common for decades? No.