That's not entirely correct due to the nature of Sandhill station, and its island platform, where have two platforms feeding from one access stairs and lift etc.
This reduces the capacity available to waiting on the platform and increases the risk of congestion: each of Kirkdale's platforms are similar width to Sandhill's.
Currently, you have three stations distributing passenger numbers (add Bank Hall), so you also reduce the flow of passengers in one direction to the station.
As I've said before, the projected waiting times for a train have increased dramatically, so there will be an impact. Another station would alleviate this!
As
@Davideeyore said, you would get a natural flow of passengers in different directions, and potentially double the amount of platform space available.