Wholehearteadly agrees with Johnathan
With all due respect:
In 5th Ed, all non-indirect spells affecting someone need to penetrate. This is the general rule, and, as such, it isn't restated in every spell description, such as Pilum of Flame, Call to Slumber or Circular Ward against Demons.
It stands to reason that, should an exception exist to that general rule, it'd be stated clearly, as is the case for indirect ReTe spells such as Invisible Sling of Vilano. You'll find no such rule for the Aegis. Thus, why should it be an exception to the general rule, when it isn't stated to be one? I mean, where do you see written "Aegis doesn't need to penetrate"?
Now, used to previous editions, some people (myself included! I remember my surprise when I discovered this) originally didn't require Wards to penetrate, nor Aegis, thinking that was RAW, despite an exception being ever stated.
As the Wards topic brought much, much discussion and controversy, it was clarified in HoH: S ("Like any hermetic spell, these wards must penetrate"). That wasn't enough, some people still thought that they didn't need to penetrate, so that was clarified again in Legends of Hermes. You say it yourself: Clarified, not errata'd 
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It is the same thing here. The fact that it is by far the most common HR doesn't stop it from being an HR .
You're almost right, though, as, originally, it seems it wasn't supposed to need penetration, but, as it worked fine with it, it wasn't errata'd to be an exception.
Ah, yes! Mercurian get WC equal to their highest ritual. I had forgotten that 
For the record, as I am way too tired to check how that applies or not here, an error I learned the hard way: By Ars5 rules, Inventing isn't learning.
That is, to invent a spell, you start from scratch, gain 1 point per lab total > level, need to accumulate a number of points equal to its level and thus to double its level to learn it in one season. Both Inventive Genius and your specialty applies
To learn a spell, you use a lab text, and need a lab total > its level to learn it in 1 season. Neither Inventive Genius nor your specialty apply.
I think your specialty is a better one than "learning spells" (I took the same), but you might prefer it.