On time sequence: you're not comparing the entire journey. Xi'an city to the airport can be as much as 1.5 hours' drive, then you need to be at the airport for check-in and security, an hour ahead. So that's 2 to 2.5 hours there, plus the flight, plus getting from PEK into town to your hotel (45-60 minutes depending on location). All total, you're looking at about a 5.5 hour sequence and that's if there are no air traffic or weather delays on either end...which is not a good bet to take with PEK as an origin or destination, where hour-long delays are routine. By comparison, the train station (Xi'an North) is in the city, as is BJ South station. Say 30 minutes in each city to get to/from station to hotel, plus arrive at station in Xi'an about 20 minute' before departure, and you're looking at total of less than 7 hours' sequence with almost zero chance of delay or weather disruption.

As to ticketing, why do you think you need to speak or read Chinese to get a ticket? The ticket for Xi'an-Beijing can be advanced purchased in Shanghai where you have host, colleague, or hotel to assist you, if you don't feel you can manage the purchase on your own.