Well understood by whom? The ScotRail staff? If a fitter can't fix a speedo fault but a driver can walk up and fix it on the spot (which has been a regular occurrence from what has been posted on here), that suggests there is a big gap in equipment knowledge and understanding. Other operators are able to deliver the service and have been doing so consistently (Cross Country, EMT, LNER) and there are more than enough power cars on hand for ScotRail to have 10 sets out on a daily basis.
Regardless of how new or old a train or any other machinery is, if the operations and maintenance crews don't know how to properly diagnose and fix issues, they are not going to work well.
What we also need to remember here is the maintenance teams were really good at looking after 170/158’s.
They don’t suddenly become useless if they aren’t delivering on the HST then there is a reason that can be fixed.
it just needs someone to work out what training or support is needed.