The cheaper Southern fare only exists because some politician or civil servant in the 1990s arbitrarily decided to allocate some services to one operator and other services to another.So why should passengers be disadvantaged just because some politician or civil servant in the 1990s arbitrarily decided to allocate some services to one operator and other services to another?
It is quite simple. If you have a TOC-only ticket, you wait until the next train provided by that operator turns up. If you have a ticket via a restricted route, you wait until the next service on that route. (It might be different for the last connection of the day, but until then, this has to be observed.)
It is easy to suggest that this gives the railway a bad reputation but equally it has enabled some people to have cheaper fares for a time. As I note, the ultimate answer will be to remove the restricted tickets and align fares between different routes.This is typical of the nonsense that gives the railway its (deservedly) crap reputation.