Are we giving the main universe Ancient One the 2-C feat, or are we making a page for the alternate universe Ancient One and only mentioning it on that page? Unlike Strange, the alternate universe Ancient One didn't show any fundamental differences in her character to suggest she has any real divergences from her main universe counterpart, so it seems weird to assume there's a major power gap between them.
Either way, it should probably be noted that the Ancient One had to draw energy from the Dark Dimension in order to split the timeline, and I believe it was already established in the Doctor Strange movie that the Ancient One used Dark Dimension energy to lengthen her lifespan and increase her power, so I think the Ancient One only scales to 2-C when amped by Dark Dimension energy. I don't believe this should directly scale to any other sorcerers, considering main universe Strange, unless I'm forgetting something, hasn't used Dark Dimension energy (and probably wouldn't in character) and even Kaecilius and his Zealots, who did use Dark Dimension energy, could not use it nearly as well, considering Kaecilius needed three other Zealots to perform the ritual to draw upon the energy, while Ancient One could draw upon it without help from others. In addition, the Zealots were very outmatched by Ancient One and Kaecilius only killed her by catching her off guard.