Both are beneficial to anybody depending on their goals, the same way the barbell row and the seated cable row differ for the back and in a broader picture, the difference between free weights (stabilisers etc blah blah) and cables (which apply constant tension).
I tend to use pullups (and barbell rows for back) for strength and power, focusing on lifting as much weight as possible with the best form possible aiming to get the most out of strength and myofibrillar hypertrophy. (Type 1 fibres)
Cables on the otherhand, specifically the lat pulldown (and the seated row), i aim to lift the weight as controlled as possible, contracting the shit out of the muscle im trying to target and stimulate as much sarcoplasmic growth as possible. (Type 2 fibres).
Taking that into account, you can see why the people (the bro's) who use the lat pulldown and swing the entire weight stack up as the heave their body back and forth dont actually have any substantial back mass. And also why those who shy away from any serious weighted pullups also stuggle to display any substantial back mass.
Well thats my thoughts on pullups vs pulldowns.