unbalanced?

[Economizer]

Because SCH isn't meant to replace WHM in content where a WHM is needed.

Ha!

(Okay the second part I don't quote is a good point, but in the majority of situations where procs aren't involved a SCH can replace a White Mage.)

not sure why sch has access to tier V nukes at lv99 yet only up to tier IV cures

As experienced healers will tell you, in the majority of situations a White Mage never casts Cure V. Cure III and IV are the main things to cast.

Given that Cure III and IV cure roughly 450 and 850 HP a piece even in only decently geared White Mages, they heal enough to do it all, and they're more MP efficient then Cure V by a fairly wide margin.

I'm sure you could get a Red Mage to complain to you that they only heal roughly 430 and 810 HP with their Cure III/IVs, and they don't get Afflatus Solace (the more terrible ones will complain about said White Mages being able to use Convert without realizing they're all WHM/SCH).

But these Red Mages aren't Scholars. They don't get Light Arts Regen buffs, they don't get Regen III let along Regen V, and they don't get Aurorastorm (you know who also doesn't get Regen V, Light Arts Regen buffs and Aurorastorm? White Mages).

Let's first focus on that light weather buff. Aurorastorm with your obi and your Twilight Cape should give you a 15% multiplicative boost to cures. This means your Cure III and Cure IV will be doing roughly 510 and 950 HP with just your cure potency set and capped Healing Magic skill - stack more Healing Magic skill and you can be curing over 1000 HP with a Cure IV.

As if that wasn't enough (and note that Cure III and IV with just Afflatus Solace are often enough for White Mages), you also get Regen spells that are actually worth using.

A White Mage will cast a Regen IV (their highest tier, but not Scholar's) for about 30HP/tic. With gear they can improve this to an extra 10HP/tic and net an extra 5 tics, although most White Mages only carry the AF3 gloves with provide the extra 5 tics. They can also merit it to provide an extra 5HP/tic, although they'd have to sacrifice better merit choices for it (basically, only a dumb White Mage would do this). So at best 45HP/tic Regen IV lasts 75 seconds or 25 tics and wastes valuable merits and a slot of inventory space. And on top of all this, it isn't MP efficient compared to cures!

A Scholar on the other hand walks in with a Regen V that they can Accession, Perpetuance, get Light Arts buffs on, and even get an even bigger boost under Tabula Rasa. With just a standard cast it cures 69HP/tic while using Light Arts and the correct gear, and lasts 36 tics. Run the strats on it and you're taking a single cast for the whole party and the spell lasts 90 tics (about four and a half minutes). Thus stratagems will make this spell will even wipe the floor with White Mage's single target cures under ideal conditions in terms of MP efficiency, and the tics do cure enough to lighten healing load.

I'd also like to take this opportunity to remind players that Cure VI sucked before the cure formula changes, sucks more now because they actually nerfed it despite it sucking then, and now Cure V sucks by comparison to Cure III/IV for White Mages.