Not really. Firstly, planes need to be spaced after takeoff more if they are larger (eg a A380 will require more spacing than a 747). This cuts the capacity gai

Not really. Firstly, planes need to be spaced after takeoff more if they are larger (eg a A380 will require more spacing than a 747). This cuts the capacity gain somewhat. Secondly, not all gates can take larger aircraft. Thirdly, larger aircraft take a lot more time to turn around than smaller ones (fewer doors per passenger). Which means your gates are tied up for longer.