I think Shield for int is fine and here is why I think so.
A normal luk mage will eventually be on par or even beat a lukless in the long run.
1 point of luk can be considered a conversion to 1 point of int and vice versa if going luk build.
The stats from equips will eventually make up for the difference in my opinion.
With the evil wings build this is a rough estimate: +15 luk from zhelm(converts to +15 more int), +5 overall, +5 gloves, +5 shoes. Evil wings has 22 more matk than lama.
Which is about 52 bonus stats of luk/int/matk that can be put to use for luk mages. More luk boosts the lower end of the magic damage like a mini mastery. And non-priests have elemental amplification(Unsure if it applies only to staff matk or total matk or total magic).
As far as the more int, that should only apply in the intermediate phase of when adding additional luk. I think +6 mp per level wont make or break the balance of being more "tanky". Otherwise bowmen and theives wouldn't even have a chance. After reaching the appropriate luk levels both mages grow at the same rate.