When the SMN hits level 80, Evoker's Roll becomes available, a powerful refresh effect combined with Diabolos's favor, a powerful refresh effect falls upon all party members within range.
Evoker's Roll, when subbed, allows up to +3 MP/tic, with the average being +2, combined with the potential +4 MP from Diabolos's favor conjures up some amazing results.
Pretty much, the only job that can possibly match that is a Bard with Gjallahorn. And those are rare, and better off with melee.
Note: To get the most out of Evoker's Roll, be sure to stay between V and X. Aim for XI if you can, But if you get a VI, just stay there, as that's a +2 MP/tic right there.
In short, +7 potential, +6 average, refresh from a single job. Perfect for any mage heavy party.