It's not a prime choice for spinning the wheel.
The reason that mage subs are used in dedicated wheel-spamming builds is for Magic Attack Bonus, which SCH does not get natively. Fast Cast is also a nice bonus, which again SCH doesn't get. The logical pick for the wheel in the 40s is /RDM, since you get MAB I and Fast Cast I. MAB II doesn't come along for BLM until 30, making /RDM or /BLM equal as far as that goes for a good bit - likely longer than you'll be spinning the wheel in XP.
Without those traits, you're basically trading any extra INT from /SCH for 'voke n' Berserk from /WAR...not really a great tradeoff.
As a solo or lowman sub, /SCH may have uses - having B+ magic skills with arts up means actual viable sleeps and aspirs and the like, and status cures/etc to boot. That said, /DNC is a very nice subjob for NIN in those situations too, though neither sub will see its true potential until high level.
____________________________•• Isiolia - Mithra - Pandemo... Asura FU SE ••
RDM BLM BST BRD NIN WAR PLD DNC BLU