There is one aspect where flying beats trains: checking luggage. If you have big suitcases it's a PITA to get them on and off the train. And changing trains means taking the bags with you, unlike flights where bags are (usually) transferred.
I disagree; taking whatever bags you like and having access to them through the whole journey is much, much nicer than having to hand them over and hope they arrive in the right place, and potentially paying extra or even having to book ahead if you've got anything other than a standard suitcase.
Not typically for international flights, and even for some US domestic carriers. Same goes for most of the rest of the world (e.g. Asia) which is what I was actually thinking about. Brazil has free luggage mandated in law.
Even when you do have to pay in the US it is typically very generous. Larger size and weight allowance, and you won’t get dinged for being even a few kilos over. And the bottom tier of frequent flyer programs (which is usually trivial to get and keep) waives all these fees anyway. I can’t remember the last time I paid for luggage allowance outside of a trip to or through Europe.
I wish that service was more widespread. The Swiss SBB will pick up your luggage at your door before your trip and deliver it at your destinations door afterwards. For a few of course, but still.
I had that issue last time and I used a service to send my luggage to the destination. They came to pick it up at my place and delivered it to my other place.
