I have already presented comment regarding AC fixing.
For rituals: ruling certain spells from dispelling rituals effects is not new (see Quiet the Raging Winds and The Cloudless Sky Returned), so there is a precedent. It's ruled also that Disenchant is a ritual, even if it is not necessarily required based only on it's effect, and I believe this is a balance decision. So regarding that, I don't think there is a problem.
Looking at specifics. Let's consider a lvl 20 Aegis. It would always dispelled by a lvl 10 Unraveling the Fabric of Vim, or a lvl 5 RHK, as long as the magus manages Pen 20 (not that hard, casting total must be 30/25).
Lvl 25 Aegis (this is us): dispel with lvl 15/10 spell, requires Pen 25, casting total 40~35. A bit harder.
Lvl 30 Aegis:dispel at lvl 20/15, requires Pen 30, casting total 45~50.
Let's jump to Aegis 40. Dispel at lvl 30/25, requiring Pen 40, casting total 70~65.
I'm not concerned with Guttering the Home-Fires since it requires a lvl 25 spell against a lvl 20 Aegis, and it must also penetrate, requiring a casting total of 45 (reasonably high). A lvl 33 Aegis would already require a ritual GHF, and the needed casting total would be around 80.
So... is this really a problem? A low level Aegis has marginal utility against other magi anyway, it's function is to protect against low level Realm critters. A high level Aegis won't be easily dispelled. And either way, interfering with an Aegis is grounds to a charge of deprivation.
Yes, a specialized magus is capable of destroying a high level Aegis right out of the gauntlet. But a specialized magus is also capable of burning Paris alone with the right set of spells.
At the end of the day, are we going to be involved, as a covenant, in the type of story where hostile magi would find it reasonable to supress/dispell the entire Aegis at once?
Overall, while I don't see any problem with the houserule, I don't think it is really necessary. If we are concerned with that happening to us, we can spend a few seasons working together to invent a high level Aegis (or buy a lvl40 Aegis from Durenmar). If we do that to other covenants, this is going to be invastigated and prosecuted b hermetic law.
Such houserule also has implications towards rituals in general, which I have not considered in depth.