Counterexample: in Summer 2019, I took a one way flight from Rome to Lisbon via Ryanair for $57.40 USD / ~€48.77 (current conversion rates, my receipt was denominated in USD).
That's a 1,160 miles / 1,870 km / ~2.75 hour flight (distance is as the crow flies). A train cannot compete with that. Not that a reasonable train itinerary between Lisbon and Rome exists.
For May 2021 [0], I'm seeing several roundtrip itineraries between Lisbon and Rome for USD$31 / €26 on Ryanair. I think the fact that such a low-priced flight can exist is actually a triumph of capitalism.