My reading of it is as independent effects.
Blade of our Lord = d10 (Mi) damage
Gladius of Light = d6 (Primary) damage vs Undead
The d10 and d6 are both weapon damage die, so use the highest (stacking rules).
It gets a bit murkier against undead. My reading would be: d10 (Mi)(Primary) for the damage (due to the stacking issue).
The Adaptations would be the biggest advantage of an advanced spell;
+9 CTN gets you a Speed 5, damage d12+3 (Mi) weapon with an additional (Primary) vs undead.
Quote:
Adaptation: Increase the CTN by 3 to increase the blade’s quality to a Exceptional weapon, thus reducing its Speed by 1 and increasing the damage by 1.
Adaptation: Increase the CTN by 3 and Strain by 1 to apply a Die Bump to the damage die. This Adaptation may be applied multiple times.
For "Yarris' Guard Against the Unnatural (Tendrils of Water + Gladius of Light)", same issue.
d8 (Primary + die bump) + adaptations vs undead; due to stacking rules on two (Primary) die.