And, honestly, I don't think even True Magic is servant rank A, because I would expect a servant of that rank to be able to do multiple things that we would call "True Magic".
Actually True Magic would be EX, probably on the servant scale, because what you can do with it is ludicrous and completely outside the rules of the game to begin with.
Lets just put the examples out there:
Zelretch defeated one of the top 2-1 beings in the entire setting, someone who could literally destroy all life on earth with 5 limbs tied behind his back, using the Second Magic.
The Grail, which can reach the root and call long-dead heroes out of the universe's storage room for cool people, is a tiny,
tiny bit of the Third Magic.
Aoko can literally reverse someone's death using timey-wimey shit and manipulates so much power in the process that Touko is afraid that
reality can't handle it.
Lorelei approaches this level of power with kiddy-grade Magecraft. Let that process through your head for just a moment.
A-rank human, perhaps. A-rank servant means high-tier Age of the Gods magic, the sort that has only been possessed by a handful of people throughout history. Nasu made it perfectly clear that modern humans aren't on the level of ancient ones in terms of magic, I don't recall him saying "but Lorelei is an exception".
Age of Gods Magecraft isn't supreme, however, we've seen that already. Zero Caster's Noble Phantasm, which is literally just a strong spellbook, can lolnope Age of Gods Magecraft by overpowering it with more prana.
Prana < More Prana is a universal rule, whether not you got old cool shit or not doesn't make it different.
Also someone can easily have A-rank Servant Magecraft in canon and not have it be "AoG Speshul" shit. Avicebron has B-rank Magecraft (Numerology). I repeat, a 12th century Magus can almost reach the same level as "high-tier AoG Magecraft". And that's without mentioning that he can build Adam, a Golem that would steamroll 3 Medeas.
Anyway I'm not having this stupid argument again. You can believe what you will but it's not influencing my sheet.