It really depends on your airport design. Schiphol and Brandenburg both have a single centralized departure / arrival hall, with a train station right underneat

It really depends on your airport design. Schiphol and Brandenburg both have a single centralized departure / arrival hall, with a train station right underneath it. Using public transport is by far the fastest and most convenient way to get to or from the airport. A lot of other airports simply aren't designed for convenience, but that doesn't mean that it isn't possible with a different design.