[Twan]

Putting everything has nothing to do with it.

To cast master Enslave (without losing communion slaves) you need 6 mages (one casting LoNS, 4 slaves, master with S5 and matrix).
To cast Undead Mastery you need the D7 guy summoning your tartarians.
You need one more S mage for antimagic.
To cast Rain of Stones you need one rare indie mage (adept of metal order) or one tartarian titan with their most common paths, or any E3 mage empowered A1.
To cast something protecting your mages against rain of stones you need one E4 (army of...) or one A4 mage (fog warriors).
To block ennemies in castle gates you need 20 or so heavy infantry or living statues, and a storm to make fliers useless (staff on one commander or cast by a mage).

Total : the fight would have been exactly similar with just the 10-12 mages with the needed paths + say 30 hoplites. It's far to be "putting everything" a nation has in endgame (the only difficulty is gathering mages with the good paths). I remember games where I could have defended half my forts with that at the same time.

My additionnal mages have only dammaged my own troops (one casting wrathfull skies on my non-shock resistant army), and my SCs never reached the ennemies.