Someone who spends the better part of the game levelling up as a physical class will still pack quite a physical punch, even if they switch to a mage class.
And if I'm not mistaken there's more than a few Support Abilities that let party members equip out-of-job-class weapons or retain Monk-like punching power.
There are some videos on nicovideo.jp of somebody actually playing FFT with a party of 4 female White Mages with those ability and weapon options. Apparently that was the inspiration for this image and several others like it by various artists on Pixiv; several of them specifically link to those videos.