Barring that Astrologian already has Gravity (and the dumbest pun in learning it) this would require Square to allow us to have some of the other spells you've mentioned. Slow only ever seems to be as a side effect and doesn't affect attack speed, only movement speed. Haste and a proper Slow seems strictly the purview of monsters and NPCs, like the Company chocobo. Meteor... is a mage limit break. The level 2 one I believe.