I found that whilst the duration of the flying time was considerably shorter than the train trip the overall flying time was still quite long given all the rigmarole at the airports and getting to and from them.
I found that traveling this intercity circuit on the Mozart much more enjoyable and relaxing than flying even though the trip took typically between 13 and 14 hours (Wiki says 13h10), the food was quite excellent (for a train) and the trips were in the daytime so there was much scenery to look at. When not doing that I could occupy myself with written/paperwork work or read a book and not be interrupted. What was really excellent about the Mozart was that it was not only an intercity train but also it took me directly to the very heart of both cities—there was no need to travel to the outskirts of the cities to their airports (I've always found traveling to and from airports a nuisance and pain so I've always considered train travel a great advantage over flying (except when flying exceptionally long distances, intercontinental, etc.).
I've not done that circuit for quite some years now and I'm sorry to see the Mozart service terminated. After reading the article I did a check on its replacement service and it seems that now a section of the trip is by TGV and that there are now two changes between the cities. Despite the introduction of the TGV, the travel time between Paris and Vienna is 13h15 — which is all of 5 minutes longer than the nominal time taken by the Mozart. Shame really.
Nevertheless, I cannot help but believe that Europe's investment in passenger train transport will pay off handsomely. When I was doing a lot of traveling around Europe by train I found most of the services quite excellent—much more so than in Anglophone countries—and I reckon that the main reason for this is that culturally the Europeans seem to be much more at home with and adapted to train travel. As such, it's very unlikely that that investment in trains will be wasted.