Making SCH in this respect risk making them to potent compared to their originals. As a SCH I feel that the concept behind their class should be magic manipulation rather then stances which enhance effects. It worked in XI cause to an extent their lack of magic skill did help to balance them out but in this game we don't have a grade lv for magic or weapon skills so it becomes harder to create a class based on the aspect of being one that can control both classes of magic.
When it comes to Light/Dark Grimiore perhaps one thing it could change to is a stance which allows one access to Conjury/Tharumagy only magic(magic is keyword so they wouldn't be able to use C/T abilities only magic spells). With SCH I feel the main focus should be dealt with their unique abilities such as the weather, helix and enmity manipulation spells, and perhaps even the tp regain one.
Or maybe this, the gimmick behind SCH could be it's ability to attach "additional effects" to Conjury/Tharumagy spells so it's interface would look different from the other DoW/DoM we have seen now.
For SCH we may see something like every 10 levels they gain an ability socket which they can then add an added effect to a magic spell. The abilities in question would be traits they learn as they level, so rather then learn traits that give them boost they would earn traits which are actually magic modifiers.
So let's say
10=1
20=2
30=3
40=4
50=5 spells you can customize
Though it would go like this
10=1 spell with one socket
20=2 spells with one socket each
30=2 spells with one socket and 1 spell with 2 sockets
40=2 spells with one socket and 2 spells with 2 sockets
50=2 spells one socket, 2 spells 2 sockets, 1 spell 3 sockets
Then based on the traits you learn you are able to enhance your abilties accordingly which may range from increases dmg, increased potency, increased casting time, reduced recast time, more mp=more dmg, or even the ability to add a combo effect to the spell.
Let's say a lv 27 trait is called "Combo"Dia" Resist down" When you add this to an elemental spell and perform dia you'll be able to combo Dia+elemental spell and grant an elemental resist down based on the element you used. Or they could also have "Combo Bio "removes dmg and replaces with element att down enfeeble" which would reduce the elemental potency of x magic they have. So if you are facing off agaisnt Garuda, if you want to weaken her wind potency you would combo Bio+Aero and the aero would perform a chance to enfeeble it's magic att rather then inflict dmg.
To me I just feel like a Scholar is all about magic manipulation, they are aware of the art behind both schools but rather then focus on being the best at both they instead train in adding their own rituals to the spell in order to increase their potency/effects. With this concept SCH would not have the same variety of a conjurer/Tharumage would have with their spells but they would have the opportunity to manipulate spells to add their own flavor to them whether they be support or offensive.