I've been flying a variety of aircraft ranging from the standard aging basic trainers 7GCBC/PA28/PA38/C152/C172 to a shiny whizbang G1000 fully integrated/automated C182T. (timzsta - so it's not a c15x....but close :-) )
My expectation is that I need to be able to navigate with the minimal amount of reliance on the aircraft's systems this effectively means map, compass, ASI, timesource.
Why, oh why. I just don’t get to grips with this. However I accept it may be because you are new to aviation.
Aviation and sailing are completely different worlds in some ways. (Very similar in others).
In both yachts and aircraft GPS systems have improved enormously in terms of reliability. The Garmin unit I use has worked faultlessly for over 1,000 hours. If you follow certain basic rules concerning installation the kit is more reliable than most panel mounted stuff.
You should also appreciate that many panel mounted GPS are fully certified for en route navigation and for approaches. That sort of certification does not readily come about in aviation (
) unless the powers that be are really satisfied that the kit is reliable.
With a G1000 I have two independent certified panel mount GPS systems and as it happens I have two handheld GPSs in my flying bag. That is one hell of a lot of redundancy. I can only imagine a loss of GPS navigation if the signal is corrupted in some way.
In that event I still have two VORs receiver, and NDB receiver, and a DME.
When all of that fails I have two radios and one hand held to provide steers from whatever D and D, FIS, or RIS service that might be available.
.. .. .. and if all of that fails I suppose I could get our my pen, paper and map.
Compare that level of fit and redundancy with a typical yacht.
Moreover, and importantly whilst accepting that most of the GA fleet is not where near as well equipped, when you are 1,000 miles offshore en route to Barbados with the rally fleet you have no way of calling up for a fix and a steer.
Your expectation of having to navigate with minimal reliance on the aircraft systems is unrealistic in anything with a reasonable fit of navigational equipment - in 1,000s of hours flying it will not happen.