I don't think network security is the issue here. Storing plain text passwords is likely a legacy problem, not an active implementation decision. And especially

I don't think network security is the issue here. Storing plain text passwords is likely a legacy problem, not an active implementation decision. And especially because some systems within the network can be vulnerable, locking down the network as much as possible at every possible point is even more important. Core banking systems can only run on 50 year old code because you have to get through many layers just to get close to accessing them.