[CUnknown]

I think we should take another look at the numbers real quick.

Clam/fetish hoarding: Costs 10 gems, gives 1 a turn. This will repay itself in 10 turns.

Soul contracts: Costs 80 slaves, gives 7 slaves a turn. This will repay itself in.. what was it? 11.5 turns?

So, in reality (not including any additional bonuses), clams are actually a better investment, but the problem is they don't give you the finished product. You have to spend a character action to actually use what you get, as opposed to Soul contracts, which don't require this.

Yet, as others have pointed out, Soul contracts have the downside of inflexibility. Once the appropriate counters are in place, you might wish you had spent those blood slaves in another way.

So, Soul contracts have advantages and disadvantages when compared to clamming/fetishing. Seems balanced to me.

Whether devils are actually worth 7 slaves though, is a different question. They may be worth more...so possibly Soul contracts are unbalanced after all, even compared to clamming (a strategy many think is unbalanced). We'd have to compare stats of similar summoned units of the same research level for that.