No, this isn't good math.
Eurostar train tickets between London and Paris are usually more expensive than flying low-cost airline. People splurge on train in preference over air, not the other way round.
True, train take s 2.5 hours of moving and fligth 45 minutes of flying. But I can get to Kings X in 10 minutes on tube and be there 20 minutes before departure and on the other end I am at Gare du Nord, smack in the centre.
When flying, it takes me 1 hour min to each airport, then I need to pay the terrorist task by queing for another hour. Then we fly and then it is again 1hour min from Orly or CDG to get where I want.