If anybody thinks a sextant is "more reliable" than GPS
has not HAD to use one.
It takes a considerable amount of practice and talent to get a fairly accurate LOP, especially on a small craft at sea, let alone the several it takes to get a good fix. Once one has mastered the sextant, mother nature and Neptune still have to condescend to allow you to get a "sight". A 4 second error in time can produce a one mile error in navigation, so exact time is critical as well.
On my circumnavigation in the 70's, it was overcast and I could not get a single sight on the sail from New Caledonia and Bundaberg, Oz, until I had already passed through the passage north of Frazer Island. I'd have given anything for any form of electronic navigation, had any existed in those days.
Sailing today with all the electronics I can afford has diminished the value of Rolaid's stock and allows me to sleep more and work much less, especially on passages.
I love my chartplotter
and other than the ICW, it has been perfect everywhere I been, but of course, I don't know if will be perfect where I haven't gone yet.
IMO one should concentrate on learning to read the water, the colors, the ripples caused by currents and underwater obstructions and let the sextant die a dignified death. GPS
is a gift and a boon to those of us who venture out on the water and redundancy is the key to continuous navigation. And common sense!