That wasn't Agartha's head
Agartha's post-mortem goes something a little along the lines of R'lyeh wanted a secession of water provinces conquered by Agartha or he would try to get everybody to help him gang up on Agartha.
The aftermath of such extortion was Agartha butted Ermor's head with his left boot, seized R'lyeh's capitol with his right arm, played footsy with TC with his right foot and flailed his left hand in a flurry trying to stave off Abysia until Machaka could eat them.
Against any 1, or even 2 of those nations I could have mowed over, but the combination of them in 4 distinct directions and very different strengths and vulnerabilities made it exceedingly difficult to do anything but achieve a 30 turn stalemate