You want to be Magic A. The bonus skills and especially spells make a huge difference. Mages are toolboxes in 5e; it's often hard to whittle down to a top 10 spell list you're satisfied with let alone top 5.
Definitely depends what you want to do and the kind of game you run.
5 spells is plenty enough to be super effective if you are mage IMO.
You can always get more as time goes on. Every run you complete is essentially another spell. So after a five runs you will have "caught up" to where you would have been in terms of spells with starting A pick and you'll have much better skills.
Magic A nets you the most bang for your buck, karma-wise, for a starting mage. I can't see any sort of 'optimal' mage character with less that Magic A.
Don't forget Magic A gives you attributes, spells, and skills. With your layout you'd need to sacrifice a lot of edge (ouch) for things that are much less important to a mage:
Attributes A - mages honestly don't need that much to be effective
Skills B - Again, mages don't need that much to be effective
If you have Magic A your magic is done. You can take Skills B if you want a lot of skills, or Attributes B if you want a lot of attributes. You could even do Resources C if you want to load up there
I simply don't agree.. If you swapped Magic A and Skills C without doing anything else to priorities you'd gain 8 group skill points and 8 other skill points.. and lose 5 spells.. then the only further difference is your edge. Yes.. if you were to buy all those edge points it might cost you a lot of Karma, theoretically.. but If you'd rather have WAY more skills and less edge it is much better to not take Magic A. Which leads me to...
I also don't agree with your assessment that mages don't need many skills.. IMO they need MORE skills than most since they have 11 magic skills to buy.. granted the 3 alchemy ones might be not be very useful, but that still leaves 8 skills of real interest, just for being "magely". So 10 group skill points could go a long way to making you a great Mage out of the box.
On top of that.. I think Attributes are the best thing to have high at char gen since they are very expensive to raise later plus they add to many skills at once and help you survive. So I always prefer having A - Attributes whenever possible.
I don't think that every mage char has to have Magic A.. and I prefer not to for most writeups..
One thing I think makes a big difference is that we don't throw around Edge as much as others seem to, so I probably don't value it nearly as high as you do.
I also almost never try to write up an "optimal" character.
OTOH.. we really shouldn't be derailing this thread.. instead let's just say there is more than one way to write up a mage, depending on what you are trying to achieve..
Given that..
My suggestion to the OP.. is try to get an image in your mind of what KIND of mage you want to be. Are you a blow drek up type.. that likes to drop people when they look at you funny? Are you the subtle type that weaves magic to cover his teams sneaky doings? Are you a healer and support type? One easy way to get some ideas is look at the mentor spirits.. Pick something with a style that appeals to you.. Will you be a sneaky Rat? Or a bold Dragon? A healing Bear? Or a blood-thirsty Shark?
Are you a once-corporate mage.. or did you come up on the streets?
Another way I write-up chars very often is to start out with a name.. like.. Firefly.. has Levitation and Fire related spells.. specializes in Fire Spirits
Once you have a concept.. it's easier to figure out what character creation choices to make.