I don’t like that Removing the Hearth’s Keystone is so easy.
I doubly don’t like that you can dispel a ritual cast with vis by spending no resources.
I just think that’s a poorly designed way of making Aegis vulnerable. I think that there should be a way to do it, but I also think it should require a ritual and be substantially harder.
This is where I partially disagree. It should not just be harder, it should be near impossible. It should require a breakthrough, or some weird quest item, something really rare and challenging.
What makes the order the pre-eminent magical force in Europe is the Order's defences; The Parma and the Aegis. The learned magicians, Sahirs, Order of Odin, etc, are all nowhere near the Order of Herme's power because the Order works together. The Order's cohesion is held together by it's defence. It's why the Schism war was so terrible, as it undermined what makes the Order of Hermes, the Order.
Nothing in the written history of the Order of Hermes, and the written material about the Aegis makes any sense if it is easy to dispel.
The Parma allows the Order to work together, without suffering the effects of the Gift.
The Aegis allows the Magi to have a place protected from magic by those not part of the ritual.
But, note that only Hermetic Magic, in Mythic Europe can revoke either of them easily. I can think of only one tradition, among the Berbers that can revoke the Parma, and I don't think any can bring down the Aegis.
Where is this in official canon?
As far as I know Parma Magica was invented by Bonisagus.
It was one of his apprentices that managed to adapt the Cult of Mercury Ritual into the Aegis of the Hearth known by the Order of Hermes.
MoH p.31 Cultellus.
This is still a problem though. Initially, yes, the Order had to care about fringe traditions, as the Order in the early days is one of a bunch of fringe traditions. Once the Order is large enough, the other fringe magical traditions have little the Order cares for, and the other magical traditions need to be insane to attack the Order as the retribution would be terrifying. The fringe traditions may take a gifted child who would otherwise go to the Order, and they may take some vis, however what they take is small.
The loot from another covenant, the Hermetic artifacts, library, vis stores, vis income, an apprentice. They are valuable. The Order needs to protect itself from the Order.
That's why the Order has Quesitores, and those who do this are likely to get marched, since doing so is several high crimes.
That is what the spells imply: That it is more retribution than actual security that keeps the Order in order. I do think the background texts imply something different.
But I think of this as one of the basic saga variables, like vis availability. The Aegis provides the sort of security that generally requires a story event to bypass; or a lesser, after-the-fact and more violent security is offered by Quesitores and Marches. Or, perhaps, the Order is "settled" enough, or sufficiently worried about some outside force, that mage-vs-mage violence or theft is truly rare.
I tend to favor the secure-Aegis, and while magi may often want to murder each other, it's usually tricky.
Two notable
exceptions are Parma Magica and the Aegis of the
Hearth, which are based on the same break-
through by Bonisagus.
ArM5, p168
The Parma Magica was indeed invented by Bonisagus.
The Aegis of the Hearth was invented by his apprentice Notatus, and is in part based on the Parma Magica.
Notatus’ development of the Aegis
of the Hearth was a Major Breakthrough, a variable spell
based on Bonisagus’ Parma Magica
HoH:TL p27
If I recall correctly powerful magical beings can also break the Aegis, basically by bashing it in with might.
It all come down to the importance of a strong aegis as opposed to a superficial one.