Oh yes, dear old DFC... welcome back
If IO540 can not navigate from A to B across Europe without a GPS that is more an issue with IO540's abilities than a problem with the system of navigation when properly taught.
I didn't say I can't. I said I wouldn't dream of even trying it due to the potential for trouble.
VFR flights generally use Visual Navigation they look out the window and see where they are. At the lower levels this is the most accurate form of navigation.
Most accurate? Oh dear...
For crop spraying, maybe. I believe that is among your several hundred specialities (which include test flying the lunar landing module) so I won't argue with that.
Also, for an electronic system to be used as sole or primary source of navigation information it must be an approved instalation and must meet the applicable performance requirements.
Reference please... (for GPS usage under VFR)
No, don't bother, there isn't one.
I hope you are not a currently working instructor, "DFC". I had a chemistry teacher at school who ensured that a couple of generations of kids hated chemistry.