IMO, the solution to the Aegis is the solution to the lack of Mastery options for Ritual Casters besides taking Mercurian Magic, a strong Gold Cord and Cautious Sorcerer.
All these are useful to any wizard that'll cast spells "on the field", who also benefit from cool mastery options. But a Ritual Caster never casts on the field, and has little Mastery Options. He can't focus on his signature spell like other magi.
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In Andorra, we have a few masteries that are "Ritual-Only", something which, IMO, is sorely lacking in the RAW.
One of these is the Secure Ritual Mastery, which doubles the botch reduction from your Mastery (And I would see it being expandable by multiple choices).
Another one reduces the number of Vis Pawns used.
Botch of these lower the number of botch dices.
Another HR I would implement is that wizard's communion doesn't impact Mercurian Magic.
Take a Mercurian Caster who tries to cast a lvl 20 aegis, with 4 other magi.
He spends 4 pawns of vis, and incurs (1+2+5) 08 botch dices.
Assuming a gold score of 1, and a Mastery of 3, that leaves only 1 botch die. Which is manageable, and rewards the Ritual-Focused player, just as the Flambeau who focuses on PoF is rewarded by his focus.
And with Adaptative Casting, his mastery applies equally to the lvl 40 aegis, leaving "just" 3 botch dices.
A non-mercurian would occur 10 botch dices (14 for the lvl 40 aegis) and, in the same situation, would need a higher Mastery.