There are a few things that worry me here.
First, you've made spellcasting significantly stronger by only requiring one skill for it. And spellcasting is already pretty strong.
I disagree. Considering that most would have a casting stat at apex skill anyway, all it's really doing is allow the caster to be more rounded with other skills. Makes the caster stronger, but not spellcasting itself. And the advancement with Focus Items and such still has to deal with Power and Control ratings.
Perhaps with advancement over time that changes, but we haven't gotten there yet.
Second, you've made spellcasting significantly stronger by letting people defend reflexively with it. And again, it's already strong.
Agreed, I'm personally on the fence about it. But we have had a hard time finding a mechanic that would allow for the scene where Ramirez blocks the gunfire from a WCV with "I go first" speed, and various other close calls throughout the fiction.
Third, Athletics and Rapport seem more powerful than the other skills, while Burglary seems weak.
Uh... okay. There's been lots of talk about Athletics being too powerful. I won't argue that.
I consider the Core version of Rapport far more clearly defined and less powerful than it was in DFRPG.
Also, I'm not sure it's advisable to reduce the number of skill points available to Chest Deep and Submerged characters. I'd rather let Chest Deep characters get two Superb skills. And it seems wrong that Submerged characters can't make a traditional pyramid.
I agree with this.
The Fate Core pyramid is effectively equal to the 20 points of Feet Wet, even with the reduced skill list.
I think using Athletics for thrown attacks may be too useful, so Physique could be used for chucking thrown weapons up to a zone away.
If you're throwing to cause Stress, it should be Shoot. Making either of those skills into Stress causing skills should be worth a stunt at least.
Regarding magic, there are now only two stress tracks - physical and mental, so for evocation spells, wizards wont be able to blast away all day, especially if they have been mentally attacked via Provoke.And you still need Lore to be a half decent Wizard. The reflexive nature of spells is tied into the four action rules. I cant see why a wizard couldnt cast a quick shield-based rote spell (which would still cost him at least 1 mental stress). Using Will to resist attacks is just incorporating the new situational aspect rules regarding blocks and represents the wizards mental focus trying to cast the spell quickly. However, I think its entirely appropriate that you couldnt use any free invocations the spell provides if you are casting the spell in reaction to an attack. That stops players loading up a rote shield spell so that they are immune to surprise attacks.
I really don't like the idea of Provoke reducing the number of spells you can cast. That doesn't hold up to the fiction well.
In DFRPG, surprise attacks don't allow defend at all. That's why we put in a clause on the reactive magical defense that you have to be aware of the attack. Catch a wizard off guard, and he's paste.