Generally speaking, the younger (not dry behind the ears) pilot crowd truly does believe that experience in the particular flight deck crew position, makes no difference.
Sadly, they are truly mis-informed.
Yes, 300 hour First Officers can indeed do quite a remarkable job, and show a high level of proficiency, however, it takes both of the following, to make it work properly...
Proper line training,
The dedication of the younger pilot to follow directions.
If any of the aforementioned are missing, they ain't worth a damn, notwithstanding what they might think.
Fortunately, most airlines today are aware of the problems involved, and apply training standards accordingly.
IE: 'know it alls' are sent back for retraining in the sim...or dismissed.
As it should be, absolutely.