There is absolutely no reason why a suitably-trained pilot cannot make a useful crew member with 300 hours or so. The RAF put pilots in the front seat of Tornadoes, and the right seat of C17s and C130Js, with around that number of hours - and those jobs are infinitely more varied and demanding than the average airline job. The major difference is that the pilots concerned have been through a highly specialised selection system, and have undergone several months of leadership training before they've even looked at a technical textbook. With the right sort of reliable and repeatable selection, and adequate pre-flying training (as all the old national airlines have practised for many years), pilots are entirely adequate to begin first-officer duties with low hours.
Scroggs