is this a runescape reference

Yes, that's intentional. D3 is a very powerful thing to have on a recruitable anywhere mage, but a rare D2N1 can add some new spells to the repertoire.

Are Ki'zids of Tyranny actually supposed to be 10% of N1? All of the other types boost their current path, which would be D3 for Tyranny, but instead they are rarely D2N1.