The cross class system is in desperate need of fine tuning.

Some classes have absolutely pointless skills in their cross class options. (warrior sunder)
Some jobs have difficulty finding 5 useful skills to even use from their options. (pld having cast time skills making them pointless when you are getting your face beat in)
Cross class skills do not scale properly making them utterly useless. (pld using cure when it costs more mp than the hp it heals)

All in all the system is annoying to say the least and pretty pointless in most cases.