The math argues from a perspective of 30-man hordes, which is very uncompetitive for an 'always-strike-last' unit with toughness 3 and an 'okay' weaponskill.
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I think 1 of each is the right answer. If you consider 20 pts from each being a power/dispel die, and let's say 60 pts being the S5/T5 chariot you get from the deal (worth more than that in reality), and the luminark providing protection to the hurricanum, then the bound spells and buffs are incredibly cheap for what you get.