Mutt;
Aterpster, what do you consider to be the
certification takeoff flight path, do you consider it to end at 1500 feet (Note, I know that he is in FAA land

)
In the abstract of Part 25, I believe it does end at 1,500.
In the real world of 121.189 it ends at 1,500 only if en route climb can be achieved at that point ( 5 s.m. each side of centerline and in en route climb configuration).
Unlike you I am not a performance engineer.