I no longer install routes up to and including TSW 2, except for RSN (which I use with the ToD4 mod) because I still like the route and it has many dependent trains that interest me (155, 363 Red, Uacns, Falns).
I will reluctantly give up 112, 612, ICE Multi system, G6, 101, 187 etc. and all the trains included in the TSW 2/TSW 2020 routes.
I have to make some choices.
It's not a matter of space on HD, but it bothers me to have in the main menu some routes that I don't use anymore.
I haven't understood yet if the locomotive addons (like the G6) are visible in the game without having the routes connected to them installed (which are in my Steam library anyway).
I'll try to verify it as soon as I have TSW 5, since I uninstalled TSW 4 more than a month ago.