Gaea managed to banish Dormammu and Chthon is regarded above her

Gaea managed to defeat him on her own, a feat is a feat so it is also completely valid.

It seems you're an unknowledgeable fella as I first suspected, aside from condescending tone and hypocritical points as well. First off, Dormammu while extremely weakened was prior able to defeat/impression her and make Gaea his play-thing, Dorm then even proceeded to steal her Earth's energies to allow him being slowly reborn on the 616 without getting weakened by his oath(Embarrassing the Earth Goddness even more):

Another misconception spread is that Gaea much later was able to miraculously break free from Dormammu's spell, which is a load of bullshit. The overrated goddness was actually SET FREE by Clea because she couldn't escape by herself during TWO UNFOLDED STORYLINES and so needed the help of others to accomplish such thing. Gaea was literally BEGGING AND SCREAMINGfor Clea to help her:

Dormammu also had all his powers stolen by Umar for quite a time:

He later got them back, but this surely affected him by a considerable margin since Umar even got credited as helping in his later defeat:

Gaea then merged/channeled with Strange and Clea's energies, as well the energy of the entire planet(This is for those users who say that Dormammu stealing Gaea's earth energies let her weakened during their second fight, which is far from true since she drags the power from the planet again) :

Another thing, I would be fine with Gaea channeling the energy of the entire planet since it's complete part of her power-set according to the handbooks....But not merging her powers WITHStrange and most especially not with Clea, who's not an "Earth-Daughter" since she actually came from another realm/universe(The Dark Dimension) and by that wasn't born on Earth for her powers have any connection to Gaea. So yes! Gaea was amped on top of all! If not by Strange ANDClea, then only by Clea(Still an amp nonetheless):

And a funny thing is how Clea's enormously mystical potential/power has been reported in the same volume:

In fact, it's been officially confirmed that Clea's full might rival that of Dormammu and Umar:

So obviously Gaea draining her power matters a lot and just to finish with a flourish:

Dormammu wasn't even fully manifested on top of all. Maybe Gaea got some new cool feats when was together with the All-Mother(Feats while merged/amped by the Ark doesn't count IMO), but I'm not aware of any.