I agree with your general gist, but surely the constituencies of Brighton, Hove and Lewes must be areas worth fighting for. None of them are true blue but all could be won.
Fatty Soames won't inwardly give a toss. Outwardly he might make a couple of grunts about inconveniencing commuters, but if you're going to find someone towing the Tory line, he'll be close to the top of the list.
Any direct action should be aimed at DafT. People like Peter Wilkinson need to be shit right up if protests get a bit too close to home. Him and his department won't give a monkeys about protests at Victoria, Brighton, etc. Southern are just the patsies for the government, so if you want...