Nobody took ownership of “consistency” of experience across terminals. In Terminal 1, the arrival pick up was on a mezzanine floor and which is now moved to the side of the building. In Terminal 2, the arrival pickup is alongside the taxi rank. In Terminal 3, it is one floor below arrival. In Terminal 4, nobody knows.

...

One unique feature that evolved in all three Terminals was that the airside concourse was for both arriving and departing passengers. Singapore became unique in this respect because only one other airport, KLIA, has this feature.

I am sure that the security people would argue against a common concourse, but the argument can go either way and nobody is the wiser. A common concourse takes the stress out for transiting passengers, while creating a marketplace communal atmosphere, increasing retail exposure, and freeing up real estate for other uses and it is here that leadership and a sense of ownership would have made a huge difference.