I'm sure there are many reasons why those signs have been left in situ - but I very much doubt it is "incompetence".
This is one of those dreadfully over-used emotive words, usually used by people who either can't think of anything more sensible or suitable to use or are just narcissistic and want people to look at them - so which are you? And what is your professional competence to judge whether this is "incompetence" ?
Wow, someone got out the wrong side of bed, over-reaction or what?!
So when a coach is refurbed and the SWT wifi stickers, the welcome to SWT door stickers and the SWT maps are left in the advertising boards that's not incompetence and laziness? What is it then? If you are refurbing a carriage surely the 6 stickers and piece of cardboard should be factored in. Even if you haven't made the replacement sticker yet for the door sticker, you should at least remove the wifi ones. Name one reason why the SWT wifi stickers should have been left and can you imagine Stagecoach refurbishing a bus they had bought second hand and putting the bus on the road saying 'Welcome to First'?
Also the change to blue in second class is causing much confusion as most WoE guards announce First as blue and Standard as red and now you get people complaining all the time that why is First so busy, only to be told it's Standard!
As for the 159's, Salisbury depot did perform miracles but were given the tools to perform miracles with. First have taken those tools away (and key staff have left too, not wanting to deal with First destroying their depot). The internal cleanliness has dropped off dramatically too since SWR took over, but then the number of on-train cleaners also seems to have dropped. The 159's are gradually dropping down to GWR 158 level which is not a step forwards.
The decisions on holding trains are also getting more ridiculous with trains being held at Tisbury even though they could've reached Gillingham, similarly at Chard instead of Axminster and Honiton instead of Pinhoe. All of which immediately results in one train being delayed 40 minutes and often all trains for the next few hours being unnecessarily late.
The WoE line was generally a line staff could be proud of, and were, but not any more, and that's before the ridiculous timetable changes come in next May (possibly) that will destroy the line completely. People want a reliable service, missing stops to save 5 minutes when your train is always 20 minutes late is rather academic.