An academy shouldn't serve a fortress for its main purpose. If they want it to have defensive capability, build a bunker complex as a redoubt on a hill, overlooking a conventional over-the-ground academy.
For me, it seems the mangaka shifts the Reverse Cannae tactic from Illipa to this battle instead. That dialogue hints on this.
Why, probably the mangaka think it would be better to spread to one unique stratagem per battle so each battle would be exciting.
imagine pretending this isn't gay and delude self that it is yuri instead.
gtfo, read a shoujo-ai series. this is gay and cute and that is the attraction.