At least 1-C,Possibly at least High 1-C ( To gain access to True Magic, the user must bypass both Alaya and Gaia's defenses. True Magic is connected directly to the root, however the power gained from this connection is unknown)
Few issues with it, first, scrap the high 1-C entirely, it'd be low 1-C possibly 1-C like every other tier 1 thing in the verse, no "okay but the outer gods are 7/9d and so the root is that plus 1", it doesn't scale to the root at all
Second, that first point about bypassing Alaya and Gaia isn't directly related to power, in fact it's practically the opposite, the goal is to bypass them by not being noticed, this is the reason for stuff like Araya's bounded fields and plans in KnK and stuff, to try to find a path to the Root without the counter force noticing and having him dealt with
For Aoko in specific I assume you're going with "well they say she's fighting the laws of the universe, and also that the world was acting against it and she did it anyway", but there's a few issues with that. First, we see how it acted against her, the shadow unironically just tried to get her to not use it, by the end literally just begging her to stop and not cast it. Secondly uhh, you do know that all reality marbles are like that too right? Hell, general magecraft is at times
The World tries to crush them, they overturn the laws of the world and produce their own world instead, etc, using just that as a justification would be implying that all reality marbles are also tier 1.
Finally, the level of force the World uses to stop things isn't always tier 1. See: counter guardians, Shiki (non void) being sent to stop Araya, etc.
Additionally, Aoko's Magic already is considered tier 1, in hax. Because it doesn't actually have anything you'd list in the tiering or AP section, the Magic itself isn't directly hitting anyone, it's just time manip and stuff with how it's been used, this was discussed before. Also I don't think I need to say it, but Aoko herself absolutely is not tier 1 physically or anything if that was the goal.