This is where I start to get really fiddly with house rules – here are my custom spell progressions for arcane casters. I’m posting these mostly to cut-and-paste into future class descriptions (if I ever get to run an Astonishing ACKS campaign).
I’ve granted low-level spells earlier than canon. (For example, a 6th level Astonishing ACKS mage can cast 4 1st-lvl spells.) I think this helps the partial-progression classes more than the stock mage. I’ve also given some extra spells in the “off-levels”. Not a big boost, but it helps partial casters (such as specialists) a bit.
(After some reflection, I’ve boosted the “1/3 Progression” Arcane 1 casters a bit more.)