Speaking to opinion:
I like that the magic priority selection has real bite... if you can't spend karma on spells you can't just pick Magic D and spend a bunch of karma to shore it up to match what someone who picked A will have.
That being said: my opinion isn't a formal ruling.
FWIW I agree. Magic D is the 1rst Level D&D mage thats going to spend the next 4 runs just learning new spells. The Magic A Mage is going to start initiating right away but will have given up something (Probably Attributes) to pick those spells up.
Also, it's not like 5 Adjustment points are free. That's a C Metatype Priority. So A Magic with
E Metatype D Metatype, or D Magic and C Metatype to get Magic up to 6.
Edit: Derp, Edition Bleed. A Magic still needs a D Metatype to get to 6 Magic without Karma.