Those losses are on a per 100 mile basis. 2-5% per 100 miles of line (not as the crow flies mind you). Superconductors would make a huge difference if they could build a room temperature superconductor.
Exactly, when people mention losses saved by superconductors they don't mean to improve the current grid. It's to route power from the always sunny side of the planet.
No. Sorry the Mediterranean Sea separates Europe from Sahara (as well as several countries) and you can't do this practically by any means. Europe doesn't own the Sahara.
The main problem with installing solar in the Sahara and transporting it to Europe is the political instability of the region. Laying cables across a sea or ocean is already routinely done.
There's communication cables laid across the sea. There's no examples I know of High Voltage transmission with enough power to operate Europe. It's not only the instability of Sahara, but laying a cable across the sea for the transmission of enough energy to power Europe would require defense of the cables. A submarine could otherwise attack the grid and take Europe offline. This is unpractical on a lot of levels and hand-waving this as a reasonable solution is silly.
The 5% is quoted further in the article for overall grid waste. The per mile basis is purely there to compare why higher voltages for the Samer power lead to less waste.