First of all, things need not be too realistic. This is alternate Earth, after all!
Second, you are perfectly right in stating that there is a Saint for everything, and there are certainly Saints that never existed historically, though not many. But Saints in the Catholic Church (would not swear about the Orthodox Churches, though) tend to be associated with activities, not basic principles like Truth or Death. Each corporation of artisans had his Saint in the Middle Ages, for instance. But which Saint do you connect with elemental principles like Air or Disorder? This is why I like the Saint/Divine Magic association better than the Saint/Rune Magic one. With Divine Magic you tie the saintly cult/order (subcult in RQ terms) to the spells, not to the runes.
Lastly, do not forget that if you are playing in 800-1000 alternate Earth, the Orthodox Church is still stronger than the Catholic Church (they are in fact the same entity until 1054). And the Orthodox pay more attention to Icons rather than Relics, just to name one difference.