ScotRail intially tried to introduce DOO but backed down because DOO is the DfTs pet policy not theirs and agreed to compromise and introduce DCO instead.
I very much agree that from a passengers perspective there is a huge difference betwen DOO and DCO. DOO and DCO are only the same thing if the unions back down a second time. I think there would be much more public support for the Unions if / when there are attempts to turn DCO into DOO. I think the Tories strategy is working, MerseyTravel can offer Merseyrail staff a deal securing their pay and employment until 2028 and some sort of DCO compromise for Northern will be enough to make it difficult for strikes to gain allot of public support. While I think Northern would be fine having DCO for 2-4 coaches, I can see services such as Preston-Bolton-Manchester becoming 8 coach services and that does concern me, even with dispatchers at main stations.
DO & DCO are only different if the onboard staff are actually provided, which of course there is no guarantee of. And unless there is actually some penalty in the franchise for failing to staff trains with the new OBS (or whatever they get called), then there is little incentive for the TOC to make much effort. And when finances in a TOC get tight, the non-essential fluffy roles like this are the first to go.
And lets not forget that the current Southern method of working for the OBS on the new DCO trains is for them to go to the doors at every station and insert their key into the doors while they do platform duties. So therefore they can't actually spend any more time in the passenger saloon and still have to go to the doors at every station, and one with a suitable key switch, so currently not achieving one of the stated plus points of removing the Guard, which was to stop the onboard person having to go to the doors.
Also, for some routes at some times then the reason that the Guard isn't seen is because they have been told by their employer to keep in the cab where it is safe, rather than risk their own personal safety in the train with the rabble.
Whatever you call it, history has shown that as soon as there is no longer a requirement to have somebody on the train, then they soon disappear. Even Scotrail, if I recall correctly, got in bother in recent years for failing to meet the targets under the Strathclyde Manning Agreement.