I disagree. The BBEG in neutral grounds most certainly is using his spirit control for his mental attacks. Although in all honesty its a terrible idea.
There are numerous cases in the
Neutral Grounds module where player characters (on the pre-gen sheets) or other characters do/have things that are not really allowed by the RAW in YS. The mental rote is however justifiable even if you believe as I do that it is normally not supported. He has sponsored magic, and is at his place of power. Of course it does not really say exactly what he gets from this sponsored magic (besides the 2 mild consequences, which is worth at most 1 refresh), so it could easily give him psychomancy evothaum (which as I read it lets you use your evocation spirit control/power bonuses in place of control/complexity bonuses, since you use the methods of evocation and it is clearly spirit, also note Kemlerian Necromancy clearly states you can use the Thaum bonuses when doing evothaum, so I assume that is not the default).
Then there is just the balance consideration, Wizards are already strong (I wont say OP, but they are close). They already have more weapon value than anyone (if they can call up 4 shifts, they have most possible PC's beat), more attack skill than anyone (yay free +3 bonus from foci and specializations) and have the most options in combat (range, zone attacks, combining maneuvers/attacks, enchanted items for high defense). They really do not need the option to attack a defense skill that is likely lower (for most non-caster enemies discipline is lower than physical defense skills) on a track with no toughness powers.