So a 1 hour flight is comparable to a 2.5 hour train ride. However a quick check shows that, on average, it takes over 2 hours (133 minutes) to get on the plane after you've arrived at the airport. Then of course you've got to get off the plane, but we'll be generous and not count that time.

In summary, taking the train is about 30 minutes faster than flying. As for cost, well, the emissions from flying make the cost somewhat irrelevant. Any reasonable government would tax flying so it's more expensive than rail travel.

The benefit of trains (for what would be a 1 hour flight) is that you don't need to get to a distant airport and go through the usual airport nonsense. You just arrive 5 minutes early and board the train. You get off the same way, at the central terminal of a large city.