"Often levels at 6000ft"?? If I recall correctly all except one of the the Heathrow SIDs level at 6000ft and that has been the case for donkeys years.
Yup, that is what I recall as well...and we normally did just that, nearly every time, hand flown did not present a particular problem....even the First Officer could do this quite well, so....what's the beef?
DEL, on the other hand, is obtuse in the extreme with ATC demands...expect the unexpected.
Par for the course.