I dunno, I don't necessarily see Harry casting more spells through out the books. If you count Cold Days, I could easily see his "wearing out" more along the lines of:
the Mantle effecting him more
I did create this power that could be used for rote casting. In my opinion it's fairly balanced and would give you not only a little more versatility with your rotes (giving you access to one more rote), but also give you a little more staying power. This could even be upgraded with a version of refinement that increases the stress track or Lore value. I'll have to write that up and add it to the power.
Rote Mastery [-2]
Your mastery of rote spells is so efficient that you do not tire as easily when casting them.
Skills Affected: Conviction, Lore
Effects:
Mind Over Matter - You gain two additional Mental stress boxes that can only be used for rote stress. These two boxes may be used before using your normal Mental stress boxes.
Arcane Intellect - Your lore is considered one step higher when determining the number of rote spells you have access to.
Backlash can be physical stress, meaning you take a physical consequence which you recover via Recovery powers.
The typical wizard doesn't have recovery. But Harry probably does by Cold Days, so that might account for some extra spell-casting. Maybe?
That's what recovery powers are for.
Remember, you can use those to shrug off a number(depending of the power level) of Minor consequences, as a supplemental action.
Also, those powers do allow you to recover from some consequences "instantly" i.e. at a scene change. (For example like Lara's broken Arm, during the Fight with the Skinwalker in the Raith Manor in Turn Coat)
Wizard's constitution however, does not. It gives you justification to start healing, it does not make you heal any faster.
Yes, I agree with what you are saying, but if you have wizards constitution, you can recover from a minor consequence after "the next scene" because you don't really need an excuse to start healing. But if you run 3 scenes that are all the same combat, you probably don't want to allow that...but by RAW, you could...even without a recovery power.
So technically, in scene 1 you take a minor, scene 2 you still have the minor by scene 3 you've recovered. Given my example above, it probably doesn't make much sense.