Well if all you are training is Cockpit Procedures, then yeah, 64k RAM (and a a whole fake cockpit of switches and instruments) will do it.
However, if the now-more accessible techniques of simulating complex fluid dynamics and finite element analysis (to reduce, not replace physical testing) didn't save money and time in the design of aircraft, they wouldn't be used as widely as they are.
In engineering, product design and architecture, CAD isn't isn't just about visualisation (though that itself is often invaluable); it is also a whole suite of tools to help groups of engineers - often from different disciplines - work together.
At a more modest level, a man down the road from me makes wooden propellers for light aircraft. His CAD needs aren't as sophisticated (single user, standard file system), but to model new propellers and generate cutting paths for his CNC router he still benefits from a modern, consumer-class desktop.
For sure, one of the influences that has made 3D CAD cheaper is that GPUs were made in huge numbers (thus sharing the R&D and tooling costs amongst more people) for the price-concious gaming market, so on that point I will concede your point that a lot of computing power is 'wasted' on mere entertainment.