I was taken by surprise. I'm a simple man, I see spells needing to penetrate, I like it.
Consistency and preferences apart, I can stand behind "what is the game we want to play, and what the rules need to be to support that". One example is our recent discussion regarding the bonus from auras being doubled, which will favor supernatural abilities.
For the Aegis... I think that, needing to penetrate, it works well for creatures with Might 20~30. With 5 magi it's not unreasonable to get a lvl 40 Aegis with a Penetration of 35, as long as we have a ReVi expert.
Are creatures with Might above 35 a constant menace in our vision of Mythic Europe? Large enough for us to say this isn't enough? And see, I'm not saying "NO creature above Might 35". If we are concerned specifically with the Goblin King of Athlone, who has a Faerie Might of 50? Have the magi acquire an AC to him (Atheus and Gazik, I'm looking at you) and use sympathetic magic to increase the penetration against him. It won't work on his Might 35 ratkin vizir, but it won't be necessary against him either, as we can manage his might. But if we have dozens of Might 35 or higher creatures directly opposing us? Yeah, that's going to be hard. But then the more proactive way to deal with the situation wouldn't be to cast an Aegis, but to show dominance and seek allegiances. It's not that we can't be invaded, but that the cost is high, and any creature with Might 35 and above is smart enough to know there's no benefit in mutual destruction.
On another note, is this what you all are envisioning? Dozens of creatures above Might 35 as our enemies?
Now, talking numbers. The Lvl 40 Aegis mentioned above does put pressure on everyone to learn the Wizard's Communion (which I don't think is a problem) and on the main caster to increase Re, Vi, Artes Liberales, Philosophiae, Penetration and master the Aegis, and this is a problem, as it requires one player to have a very specific kind of character.
Eliminating the need (totally or partially) for the Aegis to penetrate lowers the burden on the main caster but doesn't solve the fundamental problem.
Honestly, for this particular concern, I think other, more effective options for sharing the burden among the magi involved in the wizard's communion should be looked at. Eg. allow magi involved in the communion to add Artes Liberales and Philosophiae to the CT of the main caster if the spell is already ceremonial. Allow to add mastery in the communion to the CT. And on mastering Communion, the rebuttal mastery adds Mastery x 3 to the level of the spell affected by your spell (such that a lvl 20 Communion with a mastery of 3 will count as a lvl 29 Communion).
These options (which are just examples I spitballed, no need to take them too seriously) work to both allow other magi to contribute to the Aegis effectively AND in increasing the CT, and therefore, penetration, without significantly increasing CT and potentially breaking something in other situations (I believe).
Or make the Aegis a ritual, like the Fenicil Ritual, built upon the Parma. The magi add their Parma scores, the EF is the magnitude of the Aegis, penetration calculated as usual (again, I'm just spewing ideas).
But anyway, I'm fine with whatever you guys want. As I said, I was just caught by surprise with what I understand is an unnecessary addition (and deviation from standard) to the rules.