I imagine that Ryanair's requirement for 300 hours on type for 737-rated pilots is the minimum that they consider covers type training, line training and some time on the line of a previous airline. In other words, they want people who have been operational and employed on 737s by someone else. Sim time will not count - and, anyway, who's going to have 300 hours on 737 sims (unless they're sim technicians)?!