Especially given that, if it's business travel, I expect a lot of companies aren't that big on you adding a couple days of travel time because you feel like taking the train.
In the case of the parent's scenario, it seems pretty reasonable in that you're really only talking about maybe an additional half day of travel. But that's probably about the upper limit.
This seems like a demonstration of routing issues, more than anything else. I have no idea how many changes that journey would involve, but there's no way that 55 hours to cover 1269 miles is representative of the time a train (even a clunky Amtrak train) would take to cover that distance. So this would seem to be an argument for increasing routes/services, rather than an argument that the train can't ever work.
OTOH, the flight is hard to compete with in that instance, so I suspect even with a better route, you'd likely still fly between those two places. Others might not, and the new service/route would benefit people making shorter journeys along the way.
In the case of the parent's scenario, it seems pretty reasonable in that you're really only talking about maybe an additional half day of travel. But that's probably about the upper limit.