From experience of Mel some time ago operating a 747. The most inefficient use of runway occupancy. Line up clearance not given until landing aircraft past you at holding point, no” line up after landing 737” etc. And on even severe CAVOK days being denied lineup/ takeoff clearance because of landing traffic a dot in the distance. In most other Countries you’d get at least one heavy off and in USA perhaps two, in the separation ATC seemed to require.