This might be common knowledge, but i'd quite like the Class 313 but can't afford ECW as well. Thanks in advance.
I don't own any loco add-ons, but the note is right there in the DLC description: you must have the route to use the loco.
Any legacy content require the base route. If it's tsw3 exclusive, then you won't need the base route to use the train
If you want to use the class 313, you need East Coastway. DTG haven't uncoupled tsw2/tsw2020 loco dlc unfortunately. If it's a tsw 3 loco dlc then you won't need the base route as it's basically tied to the training center as it's base route.