The only problem i see with "They were designed to be used only before we got our avatars" is the "Spirit Perpetuation Cost" merits. Why have merits for something that they intended not to be used after Avatars were obtained?

Me thinks in the long list of Summoner Adjustments, Spirits should be added to the things adjusted. They don't need major focus, But perhaps actually letting them learn the magic they should have gotten already (I.E Teir V Nukes) and give them their rightful Traits (MAB Traits) so they're not 100% Useless.

Could add a "BP" like System where it could be on a 1 min timer separate from normal casting, that when used made it cast a Nuke.

Either way, it should not be very high on the list of things needing repair as it would be a lot of effort for little reward, Development time that should ideally be spent no improving the job in more meaningful ways.