@kestrel287: yes--the fighter is having one of the precious few Nice Things they've unintentionally gotten taken away, while the wizard still has many BS things he can do outside of the many outright-gamebreaking combos he gets.
-if ruled that no native casting = 0CL, he'd be stuck to 0-level spells unless he started eating orange prism ioun stones for breakfast or something (using typeless CL bonus items like the OPIS (slotting it in a wayfinder to bring it to +0-+3 total effect depending on roll), a +4CL prayer bead, and a moon circlet (-2-+2 depending on moon phase)), letting him cast a 9th level spell with the archmage ability ONLY IF he rolled a 4 on the wayfinder stone AND it's the full moon that night, and only for ten minutes/day, which is some pretty specific circumstances and makes for a very unique character since their magic is so nebulous that even they can't predict what will happen.
-even if the effect's specifics trumped the usual spell level limitation, he'd have to stick to no-saves or other spells that don't scale with CL, since even if he gets to cast it, he'd still have no base CL for it to go off of for the effect scaling (getting the absolute minimum every time).
-whether it works with SLA CL is a whole different bag of worms; lightbringer's odd wording might allow it to work, but most others wouldn't i think?). the SLA=casting is pretty specific on what spell level you're effectively a caster of (daylight SLA makes you able to cast 3rd(?)-level arcane spells, but not 2nd or 1st level for pre-reqs like feats and PrCs.
i'm FAQing the OP in hopes that some clearer ruling will be made, but i'm kinda hoping they get to keep this option--preferably in a somewhat balanced manner (like option 1 or 2), obviously.