but that would be counter productive since we kill him in the POE, but at the same time if he sends them into the future how would he know that they could survive what if the future is controlled by the darkness? wouldn't it be smarter to correct the mistakes of the past like the Battle of the Twilight Gap where the fallen could have taken the last safe city

But see, there in lies the problem. If he sent them to the past, then how does he end up working for the Queen? If he corrected the mistakes. Unless the correction was making sure he gave himself a way to get out from under the Queens control.