What is taught in school is generally a simplification of the truth. However just because that is the case doesn't mean that the "answers still aren't clear now

What is taught in school is generally a simplification of the truth. However just because that is the case doesn't mean that the "answers still aren't clear now" -- it's just the reality of the limits of the education system (if you tried to explain every topic correctly from first principles you would never get past Newtonian mechanics). The reason why AC is taught as being "more efficient" is that if you use AC you can easily use a transformer to increase the voltage (decrease the current) of the electricity being transported. That makes the transport more efficient because of I²R power losses. The reason why AC is "easier" to transform is because the classical transformer (two coils of wire and a laminated iron core -- no moving parts and incredibly efficient) requires AC input. Most power grids do use AC because this makes the grid much simpler to produce and However the part that is missing from high-school education is that AC travelling down power lines at the same voltage as DC is less efficient and more expensive per kilometre. There are many reasons for this -- but the main ones are that the skin effect means AC current only travels on the outer parts of a wire causing higher current density and thus higher losses, the generation of RF interference, and the fact that AC lines have to transport reactive power (AC current reverses direction every half-cycle which essentially means more power loss). So the most efficient transport mechanism for long distances is to generate AC, transform it up to a high voltage, and then rectify it to DC for the actual transport (and reverse the procedure on the other side). However the rectification procedure requires expensive equipment, which is why HVDC transport is only used for long-distance power transportation.