I think the intention is that it would make supernatural abilities more difficult to use, it may not have been stated as such in the text of Aegis of the Hearth, but the intent is clear, to block outside magical effects. Chris Allen did an excellent analysis of Aegis here. In a game setting where supernatural abilities are used with full effect within a foregin aegis, well, I would be mighty peeved if the SG brings an NPC with Enchanting Music and sings most of the important covenfolk away like the Pied Piper. This is the kind of thing that magi have the Aegis to protect against: the primary purpose effect of the Aegis is that it protects covenfolk so magi aren't always called away to take care of a pesky problem.
Parma Magica has a magical effect, and it can be knocked down by spells like Wind of Mundane Silence, so the rules are much more ambiguous than you suggest. If one effect can knock down Parma, why not Aegis? Note the spell indicates that it doesn't have a Perdo requisite, which suggests that according to Hermetic Theory it should have a Perdo requisite.