Have you ever taken a PrC that loses you two spellcasting levels for a handful of defensive benefits, when you were playing a primary caster? No? Me neither. Swiftblade is good the way it is, a PrC for gishes, no need to turn it more mage-y.
I was bringing it up to the OP in the hopes that he'd think "well, they say this is what a good PrC looks like. I should strive for similar power level, balance, formatting, clarity of focus, and general awesomeness of design idea". Not "I should totally do exactly this, except change it for the sake of changing it".