The Perfect Preparation ability from Mythic Adventures grant a character the ability to cast any spell on their class list, or are they still limited to "spells known" in some way?
[RPG] Does Perfect Preparation allow a caster to prepare any spell on her list
They're Limited, though exactly how is fuzzy
The bolded part of the quote is the most relevant part. Perfect preparation doesn't change your spells known or how you acquire those spells, nor does it alter your class spell list. Unfortunately the ability doesn't take into account how vital spellbooks and familiars are to the process of learning spells for the classes it references, so it leaves this weird limbo where you don't need your spellbook to prepare spells but you still need it to know them (ditto with your familiar as a witch). These sorts of editing errors are common, and I'd actually suggest asking about it on the Paizo forums to see if it can get an FAQ.
I would avoid ruling that the character gains all spells on their class spell list if at all possible, mainly because of the overwhelming prowess of those spell lists. Yes, with enough optimization one's spells known are an arbitrary number; however, beneath that level of optimization they're a way of keeping those spellcasters manageable. Don't throw that away if you don't have to.