if you wan to put the 8 hour train ride into perspective try checking the total city centre to city centre journey of the "from Salzburg via Frankfurt" flights!
Anyway, I've found flixbus have a direct bus, it costs about €45 and takes 11 hours and 10 minutes!!! If that doesn't sap the will to live, it leaves at 01:00, and from Salzburg Sud not the city centre. Suddenly the train ride looks much more attractive.
As for "true travelers see Europe by train" , true European travellers would look at this journey and ask if there was somewhere else they could go instead!