Once again, I explained my idea about this in another Witches-related thread that can be an easy resolution for all:
I'd rather they did a compromise wherein we get both a Witch lifestate and a Magic skill for everyone to learn, not just Witches. There's already a similar structure present in Vampires, where there is a Vampire lifestate and a separate Vampire lore skill that everyone can learn, but vampires get the most benefit out of it. Having a separate Magic skill can be far more beneficial (and more superior) for Witch lifestates that naturally have magic in their veins than say some random Sim trying it out.
Personally, I'm more preferable to the fact that there are some who are just born with the magic and by and large naturally better at it. However, that doesn't mean others who weren't born with it should be barred from the magic artes simply of the fact that magic was not born in their veins. However, it'd give a possible lifestate more credence for its existence for that those who weren't born with it simply aren't as powerful with magic as those who are.