Eh, the more I think about it, I'm not convinced Shin-Ra has a huge ground advantage even. Esthari soldiers wear suits that enhance them physically, so they would be stronger than average grunts on the other side. Also, a huge portion of Esthar's infantry is made up of mechanized soldiers, so the numbers are only as limited as the resources to make soldiers (the FFVIII Ultimania mentions that the robots will eventually outnumber human soldiers).
Added to that, Dr. Odine is the world's leading authority on stuff like junctioning. If Esthar's soldiers were sent into battle with GFs junctioned, they would be on the same level as members of SeeD or SOLDIER.
The Sorceress War, by the way, doesn't accurately represent Esthar's military potential. To begin with, the Ultimania is clear that Esthar was unquestionably Galbadia's superior on this front.
Secondly, I think the FF Wiki is a bit inaccurate. The Sorceress War was not an attempt by Esthar to conquer the rest of the world outright, so Galbadia wasn't actually fending them off. The war was all about finding Ellone under the pretense of seeking a suitable girl to inherit Adel's powers. She seemed to specifically want Ellone, probably because of the time looped nature of FFVIII's story -- young Adel would have learned of Ellone and her power when she sent Ultimecia's consciousness into Adel in the past in order to allow her to cast Time Compression.
Had Adel been going for outright military domination, Galbadia would have been beaten.