They are relatively rare cases, but there are more of them since the new Skyliner came online. I'd say if timed properly (also required for the heli which is a scheduled service), a taxi to the Skyliner from the 4S Maronouchi, for example, might be as fast.

Still, the dream trip would be to go through security and immigration before boarding the heli at Ark Hills and then be taken directly to airside without the need for further formalities. I recognize the frequency doesn't currently justify that but that would really be fabulous, wouldn't it?