Well, just how many people do you see doing the BOTTOM half of a pullup anyway (from a dead hang)
For most clueless cherubs the world over, partial pullups = mid to top half of a pullup. And then they wonder where their lats are. `
And finishing the movement doesn't do all that much for your lower traps, rhomboids and biceps - not more than some heavy rowing and curling can accomplish. But you need the dead hang stretch and loading if you ever want back width, especially if you don't have wide clavicles.
Pullups are primarily a width movement anyway, so if you're going to do partial pullups, do them from a dead hang (with enough load) and go for reps. As long as the people doing BOTTOM partials are progressing on some kind of rowing/thickness work they will have at least SOME lats and upper back thickness depending on their rowing abilities.
Finally, you can always develop upper back thickness even as an intermediate to advanced lifter, but its VERY difficult to sprout lats once you're an intermediate.
Again, horses for courses.