Electric grid get more reliable with scale, not less (that's why parts of North Africa is interconnected with Europe, which itself is interconnected all the way to Russia).
Small grids (like islands) are always a nightmare to manage for that reason.
North Africa is interconnected to Europe because Europe thought that it would be a good idea to build huge solar plants there.
The project ultimately failed because long distance energy transportation is difficult and expensive, among other issues like general instability of the region.
No, this is independent: first of all the Spain-Morocco interconnection predates the Desertec project by half a decade, and survived after its demise, but it has never been designed to be able to carry that much electricity (it's barely capable of carrying 1.4GW): it cannot be used for significant export and is there for grid stability alone.
Had you read the Wikipedia page you posted, you'd have realized that they planned to use dedicated HVDC lines under the Mediterranean to carry the power, and not the Spain-Moroco interconnection.
Electric grid get more reliable with scale, not less (that's why parts of North Africa is interconnected with Europe, which itself is interconnected all the way to Russia).
Small grids (like islands) are always a nightmare to manage for that reason.