Those hypothetical scalpers will indeed have control of the pricing, but they will have no customers willing to pay what they have paid, because all customers willing to pay more will have already bought tickets.
In theory, there may have been holdouts who wanted to get a better price, as you are suggesting, who then turn to the scalpers. Those holdouts are either (a) irrational for not bidding the price they were willing to pay or (b) not actually willing to pay whatever price the scalpers want to get.
By taking this strategy of picking a demand level X and buying out all the tickets once the supply is below that level, scalpers are virtually guaranteed to lose money.
For most goods, there is no demand that is independent of price.
