I disagree,
WWW.
Properly used visual sims such as the M$ type with appropriate graphics make a very useful adjunct in the early part of nav training, in the same way a synthetic flight trainer is useful in the early parts of instrument training.
Appropriately structured & with a supervising instructor supplying background ATC, traffic etc they can shorten the time required in the a/c to develop a range of skills.
I'm not supporting using them to 'pre-fly' each training nav. route since I believe a trainee navigator also has to be exposed during training to flying tasks and demands that haven't been rehearsed.
As navigators we often have to go places that we've never seen before. Our competence level is supposed be such that we can cope with navigating through unfamiliar regions. Bit rough it that happens for the first time after qualifying...