The use of Extended Reality(XR) technologies for training is gaining popularity, and flight training is one field that has begun experimenting with the best implementation for their needs. Both Virtual Reality (VR) and Mixed Reality (MR) have been used in flight simulators, but it is unclear which is the better fit. The research question is: Which implementation (VR, MR) fits better regarding psychological and ergonomic fidelity for flight training simulation? A fidelity/validity framework is used to measure and compare VR and MR in a prototype flight training simulation. Participants from the Swedish Air Force Combat Simulation Center (FLSC) with experience in extended reality (XR) and flight training simulations took part in the study. The results showed that participants performed better and reported a preference for mixed reality (MR) over virtual reality (VR), citing factors such as ease of adaptation, movements, and concentration. The thematic analysis identified three themes: naturalness, intuitiveness, and precision. Based on these findings, MR is deemed a better fit for flight training, offering a higher level of psychological and ergonomic fidelity than VR. This study can inform future research on XR and flight training simulations and inform the incorporation of XR technologies in the design of training simulations.