Brilliant spell mastery
I think there should be "brilliant spell mastery" skill in the SOS Training too. Just like other families' spell mastery, this skill will increase your spell mastery against brilliant foundables. Since it works only in Brilliant Events, it should be cheaper. For example if it is at a line that also includes a family mastery which costs 60 field guides it most cost 40 field guides.
There should also be a "brilliant departure denial" which makes brilliant foundables depart less but it should be very cheap because brilliant foundables don't depart often and it can be only used only in brilliant events.