In that case they wouldn't be a viable alternative, would they. A train can go 500+ km/h, and with good planning they don't have to cost 10x, so you're premise does not stand.

In this case, I would not. But in the real world, trains hit none of these criteria. Sure, they're slower, but the ideal case scenario is one where they can replace short- and medium-haul flights, where the difference in speed can be made up for the extra hours spent at an airport. Nor are they more expensive - trains are cheaper to run per person and can carry a ton of people at once.

And while this depends on the train service, the comfort is generally much better - there's more legroom and the seats are more comfortable, and if they serve food on board, it's superior to in-flight food. And that's not even mentioning other benefits like no limits on luggage weight or not having to throw out all drinks before boarding.