I am going 6-1 with Sandeep and currently have some of similiar thoughts.
I do not like 3 Mages that much mostly due to having Wk4, Rg10 and 40mm bases. Sandeep is hell of a hungry master when it comes to cards, so getting furious casting work is not always feasible/worth the thing.
However, I have to admit, that at 5SS for pcs they are definately a bargain. There are few arcanists model tagged 4-5 SS worth considering for Sandeep crew.
Getting 1-2 wind gaming may be an option whwere I need pure scheme-runners (e.g. inspection), however most of the scheme-work is done by summons/borrowing Sandeep (0), so I do not see a big need for them so that I would be able to replace my mages.
Performer may be an option either, but I do not feel like taking two (especially when Sandeep has push skill too and may give it out), and taking one doest not interefere with having 3 mages.
Sanction spellcaster to my mind is inferior to mages, unless you are sure that you will benefit from his (0) singularity in the game.
So any substitution to the mages I may think of (librarians, students, shastar to stay with academic synergy) leaves me with minus 1 activation (there is a variaty of combinations of 2 good models fitting into 15SS).
But I am still planning to test a game without 3 mages.
What I like in them is:
1) They are pretty endurable for 5 SS with temporary shielding and decent stats for the pricetag;
2) With their speed/range being less then average, they still presents solid thread for someone going to my part of the table coming into the gunline;
3) I like to push my models 6-8 inches forward on the first turn by attacking it with the mage with built-in-suit-upgrade. From 2 damage 1 is normally absorbed by armor/aracane shiled, the rest may be healed by regeneration if I hit a henchman wielding warding runes.
4) With 5ss price, whenever I use a mage (DD enforcer on first glance) to walk-walk-(0) for interact to pick up head or do other scheme stuff, I never feel that I lost solid DD activation which I could use more efficently to elimiante enemy;
5) They trigger Sandeep out-of-activation-cast easilly due to suits they get for academics around.
It is a pity that there is not much activity in the topic recently.
In case anyone want to contribute, I am curious to know if anyone have positive experience with:
a) Using students (transmortis);
b ) Playing complete out-of-theme list;
c) Playing with 9-10 activations right of the start (so no expensive models)
I am also thinking to get a Hannah and test it out, as Aracane Reservioir looks really helpfull and she looks durable enough to hold the front lines, though 11SS seems like a big investments.