One has to be very careful in determining what work amounts to "value shipped". It's not uncommon to have a few persons who seem to ship all the value, while the rest.. just enable them to do so, by doing the required, but invisible stuff, like the refactoring required for the new feature to ship, or fixing the bugs that makes the customers not leave, or attend those meetings that has to be attended by someone. This is somewhat related to the 10x engineer story, sure, some are a lot better than others, but sometimes it's not entirely undue to their situation. Maybe it is a skill too, to be aggressive enough to grab the work that looks most valuable and push that through, leaving your team to do the rest.