Yeah looking at the main rules and the summoning bit, it states that a 10 dice wizard will take 20 turns to summon a 10 dice creature.
That is a long time and a hero of 12 dice should be able to win against such a creature, assuming the wizard is not slain in those 20 turns.
I think the summoning of big creatures needs to already be underway or that there must be a lot of armed occultists to occupy the heroes.
Even with my rules all that lot could only mange 4 skeletons before they were defeated.
Another thing though to consider is that a 10 dice wizard if using 8 dice would probably roll 28 which is enough for two 2 dice creatures or one 4 dice creature, the wizard could burn the last d6 to control them, the wizard would be left on 1 die, but the summoned things would be more than a match for normal people which are what the world is mostly made of.
So in the grand scheme of things a quick bit of one turn sorcery is pretty impressive.
But against a mighty hero, maybe not so much.
I plan on using Thoth Amon but he will use spells to ensorcel, obfuscate and confuse his foes, this will augment his minions.
So things like whipping up sand storms to blind the heroes, making normal arrows burst into flames mid flight and inflict fire damage, that sort of stuff.