I am curious as to why the Summoner is a spontaneous arcane caster?
The intro description describes it as a character that spends much time researching spells and arcane rituals specifically in the realm of summonings. In fact the classes main ability, the eidolon, is summoned through a 1 minute ritual. None of this sounds like someone that has an inborn innate ability to attune with and produce magic.
I know that this would wreak havoc with the existing spell progression but it seems to me to fit the concept of the character far better. besides to my knowledge the only prepared arcane caster in game currently is the wizard, shouldn't there be another one?