I don't know about Khadi, never noticed him up to now
, but I do have an objection about the value of summons for defence. As Amurites I find it very easy to defend with summons. You cast them and you have a small army defending you for one turn. Next turn, you cast them again. If you have enough mages, you can use half the summons to weaken the enemy stacks, and half to hold your lines for the expected reaction. A few fireballs and/or maelstorms also help greatly defensively.
Hek, mages with Combat promotions are the most useful units in attack and defence, being able to kill an enemy weakened by their summons.
So, as a frequent magic user, I suggest you keep creating mages. Death summons help greatly in defence(since they have fear), unless facing undead armies. Archmages with water III are also valuable in defence, since water elementals split on destruction(1 time in FFH, haven't summoned one yet in FF) thus making them capable of absorving 3 enemy attacks before complete destruction, instead of one.
To avoid micromanagement you group your mages according to the type of summon(s) you wish to cast and you have them all casting the same summon with one click.
I hope this helps.
EDIT: Also, I have noticed the dimensional sphere introduces interesting hit and run tactics with "Escape" and "Teleport".