The 365s were both getting on a bit and due to some unfortunate storekeeping lost the ability to go back on Third Rail the probable natural home.
The main problem with the 365s was they were actually owned by the government due to the novel 'Hire Purchase' scheme they were bought under just prior to privatisation. When they went of lease it was the governments problem what to do with them.
They were also 'non standard' in many ways - which the later fleets, such as Electrostars or Desiros aren't.
Wasn't there something about the 365s which caused problems with signalling unless addressed ? Electrical interference springs to mind - got mentioned on one of the other interminable threads on the 365s......
If DfT/RDG/TOCs have even the slightest of cares about the travelling public then the Class 379s would be made to work on either GWR or GN in order to make some 387s available for other work. Southern Metro is about to have the shortest formations it’s had for decades and there will be extreme overcrowding.
The cold reality is that DfT/RDG and probably the TOCs just don’t care.
Bit in bold - "cold reality" as you put it, is the railways are costing the government and therefore the taxpayer billions in subsidies.
The rail industry was completely protected during the Covid pandemic, seems incapable of modernising its working practises and reducing costs. And whilst passengers on Southern are taxpayers, the majority of taxpayers aren't Southern passengers or even regular rail users.
The rail industry - particularly on the passenger side needs to modernise its working practises and reduce its cost of operation - leasing stock to ship fresh air doesn't do that.