I hope that makes it clearer.
You still don't seem to understand.
Let's get this out of the way first. Create Boosted Artifact
IS NOT an Enchant spell. They have nothing to do with each other. An Enchant spell, in Nanoha terminology, is "I cast a spell on you, and now you have this ability for a while when you didn't have it before".
The target of Boost or Enchant spells
DO NOT need to have magic innately. It can be random Joe Shmoe off the street for all the spell cares. It'll still work fine.
Create Boosted Artifact stores the
effect of a support spell to be used at a later time. People with a charm like this are not
casting the spell used in the charm's creation; they are the
recipient of it.
If you gave Mac Boost Mastery, the effects he stores in the charms would last longer once activated than they do now because the modification is improving his casting of Boost spells. If you gave him Enchant Mastery, nothing at all would change because he doesn't know any Enchant spells.
EDIT:
After finishing this post, I think I figured out another part of where your confusion may be coming from. It sounds like you think Strike Boost is an "I give you super-strength and super-speed" spell. It is not. It is an "I
increase your normal strength and speed to superhuman levels" spell. Boosts like this can only improve some quality the recipient
already has. Enchant spells are the "You don't have this ability, and I'm giving it to you" spells.
Strike Boost increases strength and speed and works because everyone has some degree of strength and speed just from being alive.
Soul Wings (an Enchant spell) gives people the ability to fly even though they don't have the natural ability to do so.