This limit only applies to item creation, not ritual spellcasting IIRC.
Anyway, even if I'm wrong on this:
- It ain't difficult to have MT 4, even at creation. Even a starting magus can reach it with 1-2 season of reading.
- A lvl 40 casting tablet allow you to cast a lvl 40 aegis even with inferior totals, at the cost of increased fatigue. We could acquire one easily.
=> If the aegis don't need to penetrate to keep creatures out, I see absolutely no reason why most young covenants don't have a lvl 40 aegis (or better!!), with older covenants having more powerful ones. It breaks my suspension of disbelief, and, IMO, makes the SG's job harder, as it means that almost nothing can cross even beginning magi Aegis.
BTW, if the aegis was such a blatant exception to the rules that apply to every over spell, don't you think it would have been explicitely mentionned? You'll also note that almost all non-hermetic magic also needs to penetrate? So I don't think that argument is really viable.
What's more mythic?
- A young magi, fresh from gauntlet, taking a casting tablet while his sodales wait besides, casting a spell mighty enough to keep anything short of a big dragon at bay?
- A band of young magi all engaging in wizard's communion, to cast an aegis able to keep moderate creatures away?
Not that this is terribly important: in most games, the magi are out of the aegis anyway