Agamotto can likely be assumed as = Strange and Dormammu, he's a sorcerer supreme afterall
On his profile it does say that he should be above Strange since Strange uses his power/spells frequently. Not sure about this, but at least it gives a good reason for him being a possible Low 1-C.
However, the 2-A reasoning of scaling to moderately-fed galactus (who is only a possible 2-A while moderately fed because of Agamotto) is a massive error.
1. Do we know for sure that Galactus was only moderately fed when he fought Agamotto?
2. Agamotto could be upgraded to just Low 1-C, since on Dormammu's Vs Battles write-up it already says that a Low 1-C feat of his is being implied to have killed the Trinity of Ashes, who are equal to the Vishanti and threaten Eternity just by existing.
Thus, Vishanti = Trinity of Ashes ~ Eternity, so that would be a good reason for Agamotto to have the same tier as Eternity.
Also, As a young man, Agamotto faced against the Celestials with aid of the likes of Odin and Phoenix. (Avengers #1)
Not to mention, he held his own against Shuma-Gorath, and while he isn't equal to Shuma (who is supposedly far above Dormammu on his page), he should at least compare.
Also, apparently the conflict between the Vishanti and Slorioth would've seriously damaged the multiverse (2-A)
3. However, assuming that this is a Moderately-fed Galactus, then he wouldn't scale to it since it'd be an outlier if Agamotto is only a Low 1-C.
However, moderately-fed Galactus did overpower Odin, who can go up to a 2-A, and Mephisto in Hell, who can also go up to a 2-A.