Regarding Sphere-style buffs from earlier, they could either be restricted to buffs that aren't overwritten by debuffs (think Refresh or Enspell vs. Haste or Attack Up which can be overwritten by debuffs), or put at a 0-priority level (so even low-priority Slows would overwrite Haste). A possible bonus would be that even though debuffs can overwrite them, a Slow wouldn't need to be Erased + Re-Hasted, you would just Erase and the Sphere effect would take over once the negative status is gone (similar to how Aura debuffs on Abyssea NMs reassert themselves immediately after your Paralyna, etc.).

Also, a Sphere-spell doesn't necessarily have to be Self-targeted, so they wouldn't have to be worthless on stuff you won't want a RDM close to the mob on, although it wouldn't be unreasonable for the buffs to receive some sort of bonus for being 'Sphere'd from the RDM who cast them for those times where a RDM can be in AoE without detriment.