By this logic, since planes can cover longer distances in shorter times than trains, should we quit trains in favor of planes?
Then you need to factor the fact that airports are not often in easy to reach places. (exception: LCY and JFK). That applies to both ends. The times stack up very rapidly.
In theory it's 2hrs to Birmingham from Copenhagen, but that trip will take approx 5hrs when you factor in all the "early arrive" and last mile shenanigans.