Yes but your control bonuses do. So if you have foci, specializations, and the like you can break through fairly reasonably, or you know you could just counter spell the silly thing.
My biggest concern here was truthfully about non-casters and what the hell they do against a wizard with high-level matched stats... Superb in both conviction and discipline could put some pretty solid blocks out on a regular basis. Of course that's really not that much different than the high conviction wizard now who takes a bunch of defensive foci and specializations. Still a game balance issue to keep in mind.
My original concern was that super skillful (ie high discipline) type caster net you no benefits on defense. It always felt to me that the less powerful but more skillful wizards could still throw down both offensively and Defensively pretty well it was just sustaining things over more than the short term is where they ran into problems. My novels are all packed in boxes as I am getting ready to move or I would dig up the various quotes from the captain of the wardens, and the like on this. I am just trying to a solution that helps reflect that and doesn't break the game.
And before some says what about Molly my thoughts on why she doesn't count are behind spoiler warning below.
Molly doesn't count because recent events (ghost stories) have shown us had that Harry's good intentions (and maybe subconscious fears of his apprentice?) have in some ways crippled her magically. It seems pretty clear that while she may not be predisposed to learning combat magic she could have had Harry been willing to move onto something more threatening than a snowball. Personally I think this is because in many ways he always saw her as the kid he first met, but that's just my take on things. She may never say burn down a houseful of vampires all at once, but that doesn't mean zombie slicing beams of doom are outside of her reach... just Harry's ability to teach her at the time
Sigh copy paste fail edit.