Okay, let me tell you why that's bad and you should feel bad.
First off, you should be /SCH unless you have a very good reason. It has better MP management, and is the only way to get the best barspells possible, and the easiest way to get Enhancing in general. Not to mention faster recast times, which are more important then the slight casting time reduction advantage. Toss in the occasional Penury or Celerity and you have the single best subjob for White Mage, hands down. In comparison, /RDM is bad, and you should feel bad thinking about it.
You know how much a Curaga 3/4 costs for a White Mage when properly used? 0 MP. If you don't know why this is, stop playing White Mage now or start wearing the right pants. At best you'd be undercuring for your MP refunds because your party is full of idiots who don't under the concept of party positioning (y'know the folks, the ones who don't understand that "Gather together. Shellra." is code for "STAY RIGHT HERE"), you're using the wrong tier, or just the inevitable slight mismatch that still leaves the Curaga spell costing less then a single target cure.
Refresh sources gives you 20 MP/minute per 1MP/tic given. Sublimation charges 3MP/tic, but has a 30 second time when it isn't charging between usage and setting it to charge again, but charges to 25% of your max HP. Mathing that out, that's a 252 MP charge for a Tarutaru's base 1011 vs a 364 MP charge for Galka, favoring Galka for Sublimation. This would be about 53MP/minute for a Tarutaru's base HP vs. 55MP/minute for a Galka's base HP.
Refresh is 3MP/tic for cases in which you have support (although in this case, you can probably delegate Haste cycles so you can do the more important work), which will give slightly better numbers then Sublimation with 60MP/minute (44MP/minute if self cast).
Refresh from gear should at least be 2MP/tic from your body piece, although if the situation is low on refresh/temps (such as the hypothetical you suggest), you'd also be wearing some more gear to bring it up 1~2MP/tic, and macroing in other gear to bring it up to 7MP/tic when casting things other then cures or barspells. This would range you from 60MP/minute to a full 140MP/minute, so I'd imagine you'd be getting enough to give a low number of 75MP/minute (with some real work getting squeezing you even more then that).
Haste costs 36 MP if you are doing it right, and if you are in situation where you need to cover the full party with it that somehow doesn't have someone else doing it so you can spam your almost-free cures, that's 72 MP/minute. Cure costs are a bit more ticky to calculate with the refund and not being sure how much you're dumping in a minute, but based on information back from the Cure Formula Changes thread, we'll just assume something like 20HP/MP (which is fairly low unless you think Cure VI is your goto spell) without calculating cureskin, then assuming that your tank is losing something like 1000 HP/minute not counting AoE moves the mob does to your group (which are either or almost free to cure), that would cost something like 50MP/minute to cover. Compare the rough gear refresh and sublimation totals of about 130MP/minute against the rough guess of a need for 122MP/minute and you'll see that if you're not gearing like a dualbox trashmage (but by no means geared like a king) you'll do okay.
If you really have troubles with that, such as for short fights where you have to dump absurd amounts of MP, you can open a fight with a full charge of Sublimation boosted with gear and top it off with some max MP gear to open with, but I can't really think of many fights outside of Voidwatch or Abyssea that require much of that, and the ones that do would be well served by having a Bard or even just a Corsair to make things easier. Any on the ones that do, I don't think 467 MP more at the start of a fight is going to change things - since I busted out the math, any retorts I see should at least have an example of a fight that requires six people, can't have a Bard, or even a Corsair, or even a Red Mage who for whatever reason can only cast Haste and Refresh II (seriously, 2~3 minutes into the fight, a Red Mage covering Haste cycles and Refresh IIing you would negate any advantage a Tarutaru has in terms of an MP pool)
You can't gear to have 450 more HP for the whole fight if you're the tank, but you can gear to have 470 more MP at the start of a fight. A Galka might have to work slightly harder, but in no case should that MP break them at 99.
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In the interest of fairness, since someone brought up possible solutions in regard to making a Tarutaru's max MP actually matter, I'd like to counter with talk about things that make a Galka's max HP not matter as much - Migawari: Ichi, Earthen Armor, and SSentinel's Scherzo come to mind. Of course, these abilities are straight up better with more max HP, but I suppose they at least exist.