You will notice for example, a Jet2 737-300 would have a greater payload restriction at LBA than a 777-200.
This is why they had range problems with some longer destinations.

A complicated subject but useful to compare non the less.

Another good example is 767s from MAN, theoretically they should be fine, but when BA operated to LAX they often suffered payload restrictions, wheras the 747s and 777s that operate NS to Asia are generally fine.